Sweet Potato and Leek Gratin

If you are looking for a sweet potato side dish for the holidays (or anytime), try this sweet potato and leek gratin. It's a wonderful savory dish with unexpected savory flavors. 

 

This casserole, with a combination of sweet potatoes, Russet/Idaho potatoes, leeks, and pancetta is a fabulous side dish for any poultry, seafood, or meat main dish. Leftovers are great for lunch as a main dish with a salad. 

You, your family, and your guests will love the unexpected combination of flavors in this hearty and savory side dish. It's pretty easy to make, and the entire gratin can be made from start to finish a day ahead of time and reheated for your holiday dinner. 

Serve this gratin along with your turkey or roast beef, make-head mashed potatoes, green beans with shallots, orange cranberry sauce, garlic Parmesan dinner rolls, along with spiced pumpkin and apple cakes for dessert (they'd go perfectly with a pumpkin martini). For the appetizer course, Greek salad skewers and an apple sidecar cocktail won't take away your appetite. 

This recipe serves six to eight as the main side dish, and eight to ten as part of a multi-side course dinner. 

Ingredients in this Gratin:

Leeks: They bring a mildly sweet flavor. They are part of the onion family but they not pungent at all. Onion haters will not even be able to tell. 

When you are slicing them, it will seem like there are a lot of leeks, but they will reduce quite a bit while cooking. Although they are not pureed, they are the basis of the sauce. 

Diced Pancetta: It adds a bit of savory meatiness. You could also substitute chopped bacon. 

Butter and Olive Oil: For cooking the pancetta.

Sweet Potatoes and Russet Potatoes: They should be peeled and sliced about 1/8 to 1/4 inch thick. 

For the Sauce: Fresh thyme, garlic, and heavy cream. 

Salt and Pepper. 

To Make This Casserole:

First, prep the leeks, potatoes, and thyme. To prepare the leeks, cut off the dark green parts and the root end, cut the leeks in half lengthwise, and then thinly slice them crosswise. Once you've cut them, place them in a bowl of cold water and swish them around to remove any soil. 

To prep the potatoes, peel them and cut them into 1/4 to 1/8 inch thick slices. To prepare the thyme, remove the leaves from the stems. 

Next, cook the pancetta in the butter and olive oil. Remove the cooked pancetta and then add the leeks to the same pan, along with the garlic, and cook, covered, for about five minutes. Add the cream and simmer for about five minutes. Add the pancetta, thyme, and salt and pepper. 

Layer the potatoes in the baking dish, along with the leek sauce. Top the dish with the rest of the sauce and bake, uncovered, for about an hour. 

Make-Ahead:

This dish can be assembled and baked a day in advance. Let it cool and refrigerate overnight. The next day, place the casserole in a 300 degree F oven and heat it until the edges are bubbly and the interior is heated through (it's best to use an instant read thermometer). 

Individual servings of leftovers can be briefly reheated in a toaster oven or the microwave. 

Equipment You May Need:

2 to 2 1/2 Quart Casserole Dish: I used a porcelain gratin dish, but a Pyrex dish works just fine. 

Mandoline: For slicing the potatoes. You can definitely use a knife, but a mandoline makes quick work of the job. 

Holiday Side Dish Week:

Welcome back to Holiday Side Dish Week 2025. This year we have lots of side dishes to help you plan your holiday meals.

Friday Holiday Side Dish Recipes:

• Homemade Green Bean Casserole by Hezzi-D's Recipe Box
• Baked Pumpkin Rice Casserole by A Day in the Life on the Farm
• Sweet Potato and Leek Gratin by Karen's Kitchen Stories
• Smashed Sweet Potatoes and Apples by Jolene's Recipe Journal
• Keto Vegetarian Eggplant Rollatini by Sneha's Recipe
• Pear Compote by Art of Natural Living
• Creamy Baked Orzo by A Kitchen Hoor's Adventures
• Cheese Stuffed Garlic Rolls by Magical Ingredients

Leek and Sweet Potato Gratin

Yield: 6 to 8 Servings

Author: Karen Kerr

Prep time: 45 MinCook time: 1 HourInactive time: 15 MinTotal time: 2 Hour

If you are looking for a sweet potato side dish for the holidays (or anytime), try this sweet potato and leek gratin. It's a wonderful savory dish with unexpected savory flavors. 

Ingredients

• 2 large leeks, trimmed and halved lengthwise and cut widthwise into 1/4 inch slices. Placed in a large bowl of cold water, soaked and then stirred with your hand, and then drained to remove any soil.
• 2 tablespoons unsalted butter plus more for greasing the pan.
• 2 tablespoons olive oil.
• 8 ounces diced pancetta.
• 1/4 cup minced garlic
• 2 cups heavy cream
• 3 tablespoons thyme leaves
• 1 teaspoon salt, plus more for sprinkling
• 1 teaspoon freshly ground black pepper
• 1 pound (about 2 medium) sweet potatoes, peeled and sliced
• 1 1/4 pounds (about 2 to 3) Russet potatoes, peeled and sliced, placed in cold water to prevent browning. You can also slice them later, when assembling the gratin.

Instructions

1. Heat the oven to 350 degrees F and butter a 2 to 2 1/4 quart casserole dish.
2. In a medium saucepan melt the butter and olive oil over medium-low heat. Add the pancetta and cook, stirring occasionally, until lightly browned, about 9 minutes. With a slotted spoon, remove the pancetta to a paper towel lined plate.
3. Add the leeks and the garlic to the same pan and cover. Reduce the heat to low. Cook, stirring occasionally, for about 5 minutes. Add the cream and bring it to a boil. Reduce heat to low and simmer, uncovered, for 5 minutes. Remove from the heat. Add the pancetta, thyme, salt, and pepper.
4. Place a layer of white potato slices on the bottom of the casserole dish, slightly overlapping each slice, like roof shingles. Sprinkle the layer lightly with salt. Top with 2 heaping tablespoons of the leek and cream sauce. Repeat with the sweet potatoes. Continue layering the potatoes, salt, and sauce, alternating colors. Spoon the remaining leek and cream sauce over the top of the assembled gratin.
5. Bake the casserole, uncovered for 50 to 60 minutes, until golden and bubbly. Let the gratin rest for 15 minutes before serving.

Nutrition Facts

Calories

504

Fat (grams)

39 g

Sat. Fat (grams)

20 g

Carbs (grams)

32 g

Fiber (grams)

4 g

Net carbs

28 g

Sugar (grams)

5 g

Protein (grams)

8 g

Cholesterol (grams)

93 mg

https://www.karenskitchenstories.com/2025/11/sweet-potato-and-leek-gratin.html

Karen's Kitchen Stories

sweet potatoes, leeks, gratin

side dish, holidays

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Recipe adapted from Fine Cooking Magazine, November, 2001. No longer in print.