Flemish Potato and Leek Gratin with Gruyère

By AislePrompt Editorial · Published 2026-04-06 · Updated 2026-04-06

How this recipe was made — this recipe was drafted by AislePrompt's AI-assisted pipeline from technique templates and USDA-sourced nutrition data, and published by AislePrompt Editorial — see how AislePrompt recipes are developed and reviewed.

A comforting gratin featuring thinly sliced potatoes and leeks baked in a creamy cheese sauce, topped with a golden crust of Gruyère. This Belgian-inspired vegetarian recipe, ready in about 75 minutes, pairs potatoes, leeks, heavy cream for a weeknight-friendly dinner that comes together with one pan and minimal cleanup. Each serving lands at about 380 calories and feeds 6, so it slots cleanly into a weekly meal plan and pairs well with a quick salad or grain on the side. Tap "Plan a meal with the AI" below to drop this recipe into your week and send the ingredients straight to Instacart. Nutrition values are approximate, calculated from USDA FoodData Central (fdc.nal.usda.gov) — verify against ingredient labels for any health-driven dietary plan.

Prep: 25 min Cook: 50 min Serves 6 Belgian cuisine 380 cal/serving

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Ingredients

1.5 lbs, peeled and thinly sliced potatoes
3 medium, white parts only, thinly sliced leeks
1 cup heavy cream
1/2 cup whole milk
1 cup grated Gruyère cheese
3 tbsp all-purpose flour
3 tbsp unsalted butter
1 tsp sea salt
1/2 tsp freshly ground black pepper
1 tsp chopped fresh thyme

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Instructions

Step 1: Preheat oven to 375°F (190°C). Grease a 9x13-inch baking dish with butter.
Step 2: Melt 3 tbsp butter in a saucepan over medium heat. Whisk in 3 tbsp flour to form a roux, cook for 1 minute. Gradually whisk in 1 cup heavy cream and 1/2 cup milk until smooth.
Step 3: Bring to a gentle simmer, stirring constantly, until thickened (about 5 minutes). Stir in 1 tsp sea salt, 1/2 tsp black pepper, and 1 tsp chopped thyme.
Step 4: Layer half the sliced potatoes in the baking dish, then half the sliced leeks. Pour half the sauce over. Repeat layers with remaining potatoes, leeks, and sauce.
Step 5: Sprinkle 1 cup grated Gruyère evenly over the top. Bake uncovered for 45-50 minutes until golden and bubbling around the edges, with potatoes tender when pierced with a knife.