Scrumptious Brunch Casserole - cooking recipe

Ingredients

4 slices bread, crust removed
1 medium onion, minced
1 c. sliced fresh mushrooms
2 Tbsp. margarine
1 c. cooked chopped ham
1 c. (4 oz.) shredded Cheddar cheese
1 c. (4 oz.) shredded Swiss cheese
1 Tbsp. flour
1 1/4 c. milk
4 large eggs, beaten
1 Tbsp. Dijon mustard
1/2 tsp. garlic salt

Preparation

Will need an 8-inch square Pyrex pan (greased).