Ham and Cauliflower Casserole

I have been making this recipe for years, but have never gone through the trouble of measuring:) So, keep in mind these amounts are flexible, but you'll get the jist!

4 cups cauliflower florets, steamed to tender crisp (I just use a chopped head of cauliflower)
2-3 cups cubed cooked ham

1/2 cup finely chopped onion
1 1/2 cups mushrooms, sliced (we leave this out)
2 tablespoons butter
1-2 tablespoons flour (I use whole wheat)
1 cup milk
salt and pepper
1 cup cheddar cheese, grated (last time I used Monterrey Jack and it was good too!)
1/2 cup sour cream
1 tablespoon dry breadcrumbs (I use whole wheat panko)
salt and pepper

Mix chopped cauliflower, ham, onions and mushrooms, if you are using them.  Season with salt and pepper. Melt butter in a sauce pan and stir in the flour.
Stir in the milk and cook until it has thickened.
Stir in the sour cream and cheese; stir until the cheese has melted and the sauce is smooth Put ham and cauliflower in to an ungreased 3 quart casserole dish.
Pour sauce over top.
Preheat oven to 350°F. Sprinkle with crumbs.
Put in the oven for 30-40 minutes or until heated through.