Sweet Potato and Rosemary Casserole

Parmesan and cayenne ramp up this savory side

Sweet potato casseroles rule at Thanksgiving. Which is no surprise—they’re festive looking and tasty. But when topped with marshmallows (as they so often are), they’re sweet enough to serve as dessert.

So how about a savory alternative? This casserole highlights the deep, rich flavor of sweet potatoes—while rosemary adds a herbal note, Parmesan cheese provides richness, and cayenne pepper gives it just a bit of a kick.

You can do most of the prep and assembly work for this dish ahead of time (even the night before), and then just pop it into the oven when ready to serve.

Which makes it one less thing to worry about on the big day. Works for me!

Recipe:  Sweet Potato and Rosemary Casserole

This dish requires several steps, none of which are difficult. First, you need to cook the sweet potatoes and purée them. (We boil the sweet potatoes, but you could also roast or microwave them; more on this in the Notes).

Second, you need to sauté onions until they turn a rich brown. This takes about 30 minutes, but you don’t need to hover over the stove while doing it—just give them an occasional stir. And it’s an activity you can do while attending to other kitchen tasks.

Last, you need to assemble the dish in a baking pan. At this point, you can either bake the casserole right away, or refrigerate it and finish later. Convenient!

What size baking dish to use? I use a 7-cup gratin dish (one that measures about 8 x 11 inches), and this recipe fills it up a bit more than half full. Alternatively, you could probably use an 8 x 8 or 9 x 9-inch pan. I sometimes divide the dish up into individual ramekins. This recipe is written assuming you’ll be using a baking pan, but the Procedure is the same for ramekins (though you’ll probably need 5 or 10 minutes less baking time).

It takes about 40 minutes of prep and cooking to get the dish ready to go into the oven. Final cooking takes about 30 minutes (plus or minus). So figure an hour and a quarter total time for this dish, although much of that time is relatively unattended.

This recipe makes 6 to 8 side dish-sized servings. Leftovers keep in the refrigerator for a few days if stored in an airtight container.

Ingredients

• ~2 pounds sweet potatoes (3 or 4, depending on size; exact quantity not critical)
• 1 tablespoon Kosher salt for seasoning cooking water (or to taste; half this amount if using regular table salt)
• 1 large yellow onion, or 2 medium ones (you want approximately 2 cups sliced onion; exact quantity not critical)
• 2 tablespoons butter (may substitute olive oil, or a neutral oil of your choice)
• ¾ teaspoon additional Kosher salt (about half that amount if using regular salt; see Notes)
• ½ teaspoon sugar (optional, but it helps brown the onions)
• 2 cloves garlic (or to taste)
• ~2 ounces grated Parmesan cheese, divided (about 1¼ to 1½ cups tightly packed; may increase amount—see Notes)
• ¼ cup heavy cream
• 2 - 4 teaspoons chopped fresh rosemary (to taste; if in doubt, use the smaller amount the first time you make this)
• ½ teaspoon cayenne pepper (or to taste; may want to reduce by half if hotness isn’t your thing)
• ½ teaspoon black pepper
• additional salt to taste
• 1 teaspoon butter for greasing baking dish
• Fresh rosemary sprigs for garnish (optional)

Procedure

1. Scrub the sweet potatoes and cut off their tips, but don’t peel them. Place the sweet potatoes in a large pot, cover with water, and add 1 tablespoon Kosher salt to season. Bring to a boil on the stovetop. When the water begins boiling, reduce it to a simmer and cook until a paring knife or fork can be inserted easily into the center of each sweet potato. Depending on size, this can take 20 to 35 minutes. When the sweet potatoes are done, drain them and allow them to cool for a few minutes. (See Notes for alternate methods of cooking sweet potatoes).
2. Meanwhile, peel the onion(s) and cut in half through the poles. Slice thinly across the width. Put a skillet (preferably nonstick, and one with a lid) on medium stovetop heat. When hot, add the butter (or oil) and allow it to melt. Add the onions. Sauté until translucent (about 8 minutes). Add ¾ teaspoon Kosher salt and ½ teaspoon sugar, and stir. Lower the heat a bit, cover, and cook until the onions are brown (about 20 minutes), stirring every 5 minutes or so. You’ll be adding garlic to the onions during their last 5 minutes of cooking time (see next step). When the onions are done, remove them from the stovetop and set aside.
3. Meanwhile, peel and slice the garlic. Add it to the onions about 5 minutes before the onions are done.
4. Grate the Parmesan cheese. Reserve ¼ cup or so.
5. At this point, the sweet potatoes should be reasonably cool. Peel them and cut them into chunks. Purée them with a food ricer or a food mill. Alternatively, place the cooked sweet potatoes in a medium-sized bowl and mash them with a potato masher or a heavy spoon. It’s OK if a few chunks remain.
6. When the potatoes are puréed, add the heavy cream and stir to combine. Add the browned onions and the Parmesan cheese (except for the reserved amount). Add the chopped fresh rosemary, the cayenne pepper, and the black pepper. Stir to combine. Taste and add additional salt if necessary.
7. Butter a baking dish and scoop in the sweet potato mixture. Smooth the top, and sprinkle on the reserved Parmesan cheese to evenly coat the top. Cover with shrink wrap and refrigerate until ready to bake (or skip the shrink wrap and bake right away if you wish).
8. When ready to bake, preheat the oven to 375 degrees F (see Notes). If the casserole has chilled in the fridge, allow it to sit at room temperature for half an hour to warm up. When ready to bake, remove the shrink wrap and place the casserole in the oven. Set a timer for 20 minutes. At the 20-minute mark, remove the casserole to judge how it’s coming along—the sweet potatoes are already cooked, so you’re just warming them and browning the cheese on top. My oven tends to be slow, so I generally bake this dish for another 10 minutes or so. During the last 2 or 3 minutes, I often turn on the broiler and move the baking dish to the top rack of the oven to brown the casserole.
9. Add rosemary sprigs for garnish, if you wish, and serve.

Notes

• Would you prefer to use a different method for cooking the sweet potatoes? The most flavorful way is probably to roast them. You can use our recipe for Roast Sweet Potatoes, but go easy on the seasonings—you’ll be adding plenty of flavors in this dish. 
• Alternatively, you can microwave the sweet potatoes. Just peel them, cut them into chunks, and microwave them in a microwave-safe covered dish until they’re soft.
• Or you can peel the raw sweet potatoes, chunk them, and boil them.
• You can even bake the sweet potatoes, then scoop out the pulp when they’re done.
• A little rosemary goes a long way. So you might want to start with a smaller amount first, then increase if necessary the next time you make this recipe (believe me, there will be a next time).
• If you can’t find fresh rosemary, I wouldn’t recommend using the dried version—I’ve yet to find a brand that has any real flavor. Instead, I’d substitute fresh parsley or thyme (you can use fresh or dried thyme; if using the dried variety, halve the amount called for in the recipe).
• Fortunately, we never run out of fresh rosemary since we grow our own (outdoors during the summer, in a windowsill pot during winter).
• The volume of Parmesan you’ll get when grating depends on what type of implement you use. A microplane produces a fluffy, airy mound of cheese, for example, while a box grater produces something much more compact. So if you’re measuring by volume, make sure to pack the grated cheese firmly into the measuring cup. Exact quantities aren’t critical, however—you can use loads more cheese if you like.
• BTW, even though this dish is basically a gratin, I don’t usually try for a super brown crust. If you want a very brown crust, though, you should really pile the cheese on top (Step 7)—and then run the dish under the broiler right before you remove it from the oven.
• I like to use Kosher salt, but if you don’t have that on hand, you can use plain table salt (though I’d reduce the amount by about half since table salt is finer and more “condensed” than Kosher).
• You can bake this dish at a higher temperature than specified in this recipe—up to 425 degrees F or so. If you go this route, reduce baking time by a few minutes.

Sweet Memories

“Wow,” said Mrs. Kitchen Riffs. “This dish is even better than your Roast Sweet Potatoes.”

“Agreed,” I said. “Even though our recipe for roasting sweet potatoes is one of the all-time most popular posts on the blog.”

“And I think this casserole works better as a side dish than the marshmallow-topped versions,” said Mrs K R. “Still, you gotta admit there’s something magical about really sweet sweet potatoes.”

“You have that faraway look in your eyes,” I observed. “Hatching a plan?”

“Well, I was just thinking,” she said. “Instead of pumpkin pie for Thanksgiving this year, maybe we should do sweet potato pie.”

“Terrific idea!” I said. “Remember the first time we had sweet potato pie together? It’s when we were moving from Dallas to New York, way back in the mid-80s.”

“That’s right!” said Mrs K R. “On the way there, we stopped for lunch in De Valls Bluff, Arkansas—and had some really terrific barbecue. Right across the street from the restaurant was the Family Pie Shop, so that’s where we had dessert.”

“I’ve been haunted by the flavor of that sweet potato pie ever since,” I said.

“That settles it,” said Mrs K R. “Time to work on my own sweet potato pie recipe!”

Am I a lucky guy, or what?

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