easy cheesy brunch casserole

Ingredients For easy cheesy brunch casserole

• 4 slice

  white sandwich bread
• 1 md

  onion, chopped
• 1 c

  fresh mushrooms, sliced
• 2 Tbsp

  butter,unsalted
• 1 c

  cooked ham, chopped
• 1 c

  cheddar cheese, shredded
• 1 c

  swiss cheese, shredded
• 1 Tbsp

  all purpose flour
• 1 1/4 c

  milk
• 6 lg

  eggs, beaten
• 1 Tbsp

  dry mustard, i prefer coleman's
• 1/4 tsp

  garlic powder with parsley
• parsley for garnish