Mushroom and Leek Baked Casserole
A creamy, comforting casserole featuring earthy mushrooms and sweet leeks in a velvety cheese sauce, topped with a golden breadcrumb crust. This american-inspired one pot ready in about 50 minutes pairs butter, leeks, mushrooms for a weeknight-friendly dinner that comes together with one pan and minimal cleanup. Each serving lands at about 450 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.
Ingredients
- 3 tbsp butter
- 1 large, white and light green parts only, thinly sliced leeks
- 2 cups, sliced mushrooms
- 1/4 cup all-purpose flour
- 2 cups whole milk
- 1/2 cup, grated Gruyère cheese
- 1/4 cup, grated Parmesan cheese
- 1/2 tsp dried thyme
- to taste salt
- to taste black pepper
- 1/4 cup breadcrumbs
Equipment for this recipe
Top-rated tools to make this recipe successfully.
Instructions
- Step 1: Preheat oven to 375°F (190°C). Melt 3 tbsp butter in a medium saucepan over medium heat. Add 1 cup thinly sliced leeks and cook for 3 minutes until softened, stirring occasionally.
- Step 2: Add 2 cups sliced mushrooms and cook for 5 minutes until they release their liquid and it evaporates.
- Step 3: Stir in 1/4 cup all-purpose flour and cook for 1 minute, stirring constantly to avoid lumps.
- Step 4: Gradually whisk in 2 cups whole milk until smooth, then bring to a gentle simmer. Cook for 3-4 minutes until sauce thickens and coats the back of a spoon.
- Step 5: Remove from heat and stir in 1/2 cup grated Gruyère cheese, 1/4 cup grated Parmesan cheese, 1/2 tsp dried thyme, and salt and pepper to taste.
- Step 6: Transfer mixture to a greased 9x13-inch baking dish. Sprinkle 1/4 cup breadcrumbs evenly over the top.
- Step 7: Bake for 25-30 minutes until top is golden and sauce bubbles around edges.
Frequently asked questions
How long does Mushroom and Leek Baked Casserole take to make?
Total time is about 50 minutes (20 min prep + 30 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 Mushroom and Leek Baked Casserole?
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 butter from drying out.
Can I substitute ingredients in Mushroom and Leek Baked Casserole?
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 Mushroom and Leek Baked Casserole 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 Mushroom and Leek Baked Casserole?
American one pot 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.
What others are saying
- ★★★★★
Swapped butter for olive oil to keep it lighter. Still delicious.
- ★★★★★
Used half the salt and it was still plenty flavorful.
- ★★★★★
Added some red pepper flakes for heat — highly recommend.
