Scalloped Vegetable Bake

Step 1 -Preheat the oven to 350 degrees F.

Step 2 -Using the extra butter, grease a 1 1/2-quart casserole dish.

Step 3 -Add the sliced carrots and the sliced celery to a large saucepan.

Step 4 -Add about 1 inch of water to the saucepan and bring the vegetables to a boil.

Step 5 -Cover and cook until the carrots are barely tender, about 8-10 minutes.

Step 6 -Add the peas to the vegetable mixture and cook, about 3-4 minutes.

Step 7 -Drain the vegetables in a colander. Set them aside.

Step 8 -In the same saucepan over medium heat, melt 1 tablespoon of the butter.

Step 9 -Add the mushrooms and sauté until they are tender, about 5-7 minutes.

Step 10 -Transfer the mushrooms to the reserved bowl of cooked vegetables.

Step 11 -Melt 4 tablespoons of the butter in the same saucepan over medium heat.

Step 12 -Add the flour and the dry mustard and cook, stirring, until the raw flour smell disappears, about 2 minutes.

Step 13 -Gradually add the milk to the flour mixture and continue cooking and stirring until thickened.

Step 14 -Taste and season the sauce with the salt and the pepper as needed.

Step 15 -Add the reserved cooked vegetable mixture to the sauce and mix gently to combine.

Step 16 -Melt the remaining 2 tablespoons of the butter in a separate, small saucepan.

Step 17 -Add the breadcrumbs to the melted butter, tossing to coat thoroughly.

Step 18 -Pour the vegetable mixture into the prepared baking dish.

Step 19 -Sprinkle the vegetable mixture with the parmesan cheese and the toasted breadcrumbs.

Step 20 -Bake until the vegetable mixture is bubbling and the topping has browned, about 25 minutes.

Step 21 -Serve.