Flemish Potato and Leek Gratin with Gruyère

By , Test Kitchen Director · Reviewed by AislePrompt Editorial · ·

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 ready in about 75 minutes pairs peeled and thinly sliced potatoes, heavy cream, whole milk 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

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Instructions

  1. Step 1: Preheat oven to 375°F (190°C). Grease a 9x13-inch baking dish with butter.
  2. 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.
  3. 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.
  4. 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.
  5. 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.

Frequently asked questions

How long does Flemish Potato and Leek Gratin with Gruyère take to make?

Total time is about 75 minutes (25 min prep + 50 min cook). Most home cooks find this fits comfortably into a weeknight; double the batch on Sunday for two dinners.

How do I store leftover Flemish Potato and Leek Gratin with Gruyère?

Cool to room temperature within 2 hours, then store in an airtight container in the fridge for up to 4 days. Reheat covered in a 350°F oven for 10-12 minutes, or microwave at 70% power in 60-second bursts to keep heavy cream from drying out.

Can I substitute ingredients in Flemish Potato and Leek Gratin with Gruyère?

Yes — most ingredients in this recipe have flexible swaps. For oil, use any neutral high-smoke-point oil (avocado, grapeseed, refined coconut). For aromatics, dried herbs at ⅓ the volume of fresh work in a pinch. The full ingredient list is shoppable on Instacart so you can see substitutes in real time.

How do I scale Flemish Potato and Leek Gratin with Gruyère for a different number of people?

The recipe is written for 6 servings. Multiply each ingredient by (your serving target / 6). Cook time stays roughly the same up to 2x; for 3-4x batches, switch from a skillet to a sheet pan or stockpot so the food isn't crowded — overcrowding steams instead of browns.

What goes well with Flemish Potato and Leek Gratin with Gruyère?

Belgian vegetarian like this pair well with a simple grain (rice, couscous, or crusty bread), a quick salad with acid (lemon vinaigrette, pickled onions), and a pan sauce or yogurt-based dip. Tap "Plan a meal with the AI" to get specific side suggestions.

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