Potato Leek and Fennel Gratin

Elevate your side dish game with this luxurious Potato Leek and Fennel Gratin—a creamy, cheesy casserole that’s sure to impress. Thinly sliced russet potatoes are layered with sweet, caramelized leeks and fennel, then smothered in a velvety blend of heavy cream, milk, garlic, and thyme. A generous topping of Gruyere and Parmesan cheeses creates a golden, bubbly crust that’s pure comfort food. Perfect for holiday gatherings or elegant dinners, this gratin pairs beautifully with roasted meats or a fresh green salad. Ready in just over an hour, it’s the ultimate make-ahead dish that’s both hearty and refined. Experience the irresistible blend of flavors and textures in this crowd-pleasing potato gratin recipe!

Nutriscore Rating: 64/100

Prep Time:25 mins

Cook Time:60 mins

Total Time:85 mins

Servings: 6

Ingredients

• 4 large russet potatoes
• 2 medium leeks
• 1 large fennel bulb
• 3 tablespoons unsalted butter
• 2 cups heavy cream
• 1 cup whole milk
• 2 large garlic cloves
• 1 teaspoon thyme
• 2 cups grated Gruyere cheese
• 1 cup Parmesan cheese, grated
• 1 teaspoon kosher salt
• 0.5 teaspoon black pepper
• 1 tablespoon olive oil

Directions

Step 1

Preheat your oven to 375°F (190°C) and grease a 9x13-inch baking dish with butter or olive oil.

Step 2

Peel the russet potatoes and slice them thinly into rounds, approximately 1/8-inch thick. Set the sliced potatoes aside in a bowl of cold water to prevent browning.

Step 3

Trim the dark green portions of the leeks, keeping only the white and light green parts. Slice the leeks lengthwise, then rinse thoroughly to remove any dirt. Thinly slice the leeks crosswise.

Step 4

Cut off the stalks and fronds of the fennel bulb, reserving a few fronds for garnish if desired. Slice the fennel bulb thinly.

Step 5

In a large skillet, heat 1 tablespoon of olive oil and 1 tablespoon of butter over medium heat. Add the sliced leeks and fennel, and cook until they are softened and lightly golden, about 5-7 minutes. Set aside.

Step 6

In a small saucepan, heat the heavy cream, milk, minced garlic, and thyme over medium-low heat until warm but not boiling. Stir occasionally. Season with kosher salt and black pepper.

Step 7

Drain the potatoes and pat them dry with a clean kitchen towel.

Step 8

Layer half of the sliced potatoes evenly at the bottom of the prepared baking dish. Season lightly with salt and pepper.

Step 9

Spread half of the cooked leeks and fennel mixture on top of the potato layer. Sprinkle 1 cup of grated Gruyere cheese over the top.

Step 10

Repeat with the remaining potatoes, leeks, and fennel. Pour the warm cream mixture evenly over the layered ingredients in the baking dish.

Step 11

Sprinkle the top with the remaining Gruyere cheese and the Parmesan cheese.

Step 12

Dot the top with the remaining 2 tablespoons of butter, broken into small pieces.

Step 13

Cover the baking dish loosely with aluminum foil and bake in the preheated oven for 40 minutes.

Step 14

Remove the foil and continue to bake for an additional 20 minutes, or until the top is golden brown and the potatoes are tender when pierced with a knife.

Step 15

Allow the gratin to rest for 5-10 minutes before serving. Garnish with fennel fronds, if desired.

Nutrition Facts

Serving size	(2817.5g)

Amount per serving	% Daily Value*
Calories	4834.5

Total Fat 315.6g	0%
Saturated Fat 182.5g	0%
Polyunsaturated Fat 2.1g
Cholesterol 881.6mg	0%
Sodium 4182.3mg	0%
Total Carbohydrate 332.5g	0%
Dietary Fiber 35.3g	0%
Total Sugars 46.8g
Protein 149.6g	0%

Vitamin D 120.8IU	0%
Calcium 3968.3mg	0%
Iron 22.9mg	0%
Potassium 9068.7mg	0%

*The % Daily Value tells you how much a nutrient in a serving of food contributes to a daily diet. 2,000 calories a day is used for general nutrition advice.

Source of Calories

Fat: 59.6%

Protein: 12.5%

Carbs: 27.9%