Baked Macaroni and Cheese

INGREDIENTS

• 1 large egg
• 1 tablespoon powdered mustard
• 1/2 cup yellow onion, finely diced
• 1 teaspoon kosher salt
• 1/2 teaspoon paprika
• 12 ounces sharp cheddar, shredded
• 1 cup panko bread crumbs
• 3 tablespoons butter
• 1/2 pound elbow macaroni
• 1 bay leaf
• Fresh black pepper
• 3 cups milk
• 3 tablespoons flour