Overnight Breakfast Casserole with Sausage and Cheese

Ingredients

• 2 tablespoons unsalted butter, (divided)
• 1 pound sweet or spicy pork sausage, (casings removed)
• 1 medium yellow onion, (chopped)
• 1 loaf ((18 slices) white sandwich bread, such as Pepperidge Farm, crusts removed and cut into 1-inch (2.5-cm) cubes)
• 2½ cups grated sharp cheddar cheese
• ½ cup chopped fresh parsley
• 6 large eggs
• 2 cups half-and-half
• Scant teaspoon salt
• ¼ teaspoon freshly ground black pepper