Overnight Croissant Recipe

Name: Overnight Croissant Recipe
Ingredients: 1 tablespoon olive oil; 1 small onion peeled and chopped; 1 pound roll breakfast Turkey Sausage; mild flavor; 4 large butter croissants or 8 small croissants; 1 cup shredded cheddar cheese; 6 large eggs; 1/2 cup heavy whipping cream; 3 cups milk (whole milk recommended) divided; 1/2 teaspoon dry mustard powder; 1/2 teaspoon salt (plus additional for the gravy to taste); 1/2 teaspoon black pepper (plus additional for the gravy to taste); 1/4 teaspoon paprika; 1/4 teaspoon garlic powder; 2 tablespoons butter; 3 tablespoons all-purpose flour