Bowl Game Breakfast Casserole - Tailgate Guru

Ingredients

• Butter, for greasing
• 2 TBSP extra-virgin olive oil
• 1/2 cup finely diced pepperoni (2 ounces)
• 1/2 pound shiitake mushrooms, stems discarded and caps cut into 3/4-inch pieces
• 1 medium onion, minced
• 1 red bell pepper, cut into 1/2-inch pieces
• 2 tsp kosher salt, plus more for seasoning
• 8 large eggs
• 3 cups whole milk
• 1 TBSP Dijon mustard
• 1 TBSP soy sauce
• 1/2 tsp pepper
• 3/4 pound day-old challah, sliced 1 inch thick and cut into 1-inch dice (10 cups)
• 6 ounces Black Forest ham, finely diced (1 1/4 cups)
• 1 cup shredded Monterey Jack cheese (1/4 pound )
• 1 cup shredded aged white cheddar cheese (1/4 pound )
• 1/2 cup finely chopped scallions, plus thinly sliced scallions for garnish