Creamy Pizza Casserole

This is total comfort food for me.  Not super healthy.  When I looked on the internet for other pizza casseroles most of them had a tomato base.  This one uses a white sauce.  I got this recipe from my mother-in-law.  There's a chance that she made the recipe up.  She also was cooking for 8 children - including 5 teenage boys.  So I had to make the recipe a bit smaller.  And since I have stopped cooking with creamed soups, I subbed stuff in for that, too.  Anyway, here it is.

Make a white sauce:
5 T. butter
5 T. flour
2 1/2 c. milk
1 c. chicken broth
Melt butter.  Gradually stir in flour.  (I add in some of my spices before the liquid.)  Pour in liquid and stir until slightly thickened.

Add: 1/2 c. sour cream

Seasonings:
1/2 tsp. onion powder
1/4 tsp. garlic salt
2 tsp. oregano
1/2 tsp. pepper
1 tsp. salt

Pizza mixture:
Cooked pasta (we like the bigger shells),
8 oz. mushrooms,
1 can olives (sliced)
1/2 lb. Italian sausage (cooked and drained)
Pepperoni (quartered)
2 c. mozzarella cheese, grated

Mix pizza mixture and white sauce together. (Mine was a bit soupy)  Put in large casserole.  Top with more mozzarella if desired.  Bake at 350 for 1 hour or until bubbly.