Make-Ahead Sausage and Egg Casserole

Ingredients

• Pepper
• 1/2 c. whole milk
• 1/2 lb. sweet Italian sausage, casings removed
• 1 medium onion, finely chopped
• 12 large eggs
• 1 10-oz package spinach, thick stems discarded
• 1/2 lb. country bread, cut into 1-inch pieces
• Kosher salt
• 2 tbsp. extra virgin olive oil, plus more for pan
• 1/3 c. chopped drained oil-packed sun-dried tomatoes
• 1/4 c. crumbled feta cheese