wild mushroom and spinach frata with smoked bacon

Ingredients

• 2 small sweet onions sliced thin
• 1 cup each of assorted mushrooms like oyster,shitake,and baby bella.
• 6 cups cubed into one inch cubes, crust too, of hearty bread,like sour dough or french,italian.
• 8 large eggs beaten
• 2 1/2 cups whole milk or 1/2+1/2
• 1 1/2 cups shredded swiss cheese
• 1 cup shredded fontina cheese
• 1 teaspoon salt
• 1/2 teaspoon pepper
• 2 tablespoons olive oil
• 4 tablespoons butter, room temperature for the baking dish
• 1 teaspoon thyme, dried
• 8 slices smoked bacon cooked crispy
• 1 package spinach, fresh,torn