Cheesy Squash Casserole

4 pounds yellow squash, sliced
1 1/2 cups chopped onion
4 tablespoons butter
4 tablespoons all-purpose flour
2 cups whole milk
2 cups shredded Cheddar cheese
1 1/2 teaspoons salt
1 teaspoon pepper
1/2 cup breadcrumbs, toasted

Saute onion until tender. Add squash and saute until squash begins to soften.

Preheat oven to 350°.

Melt butter in a medium, heavy saucepan over medium heat. Add flour; cook, stirring constantly, 1 minute. Gradually add milk; cook, stirring constantly, until mixture is thickened and bubbly. Remove from heat; add cheese, salt, and pepper, stirring until cheese melts. Add squash mixture; stir well.

Spoon squash mixture into a shallow 3 quart greased baking dish. Sprinkle squash mixture evenly with breadcrumbs. Bake at 350° for 20 to 25 minutes or until mixture is thoroughly heated.