Part of the allure of a mini Philly Cheesesteak bite is enjoying a yummy layer of melted cheese all oozy and delicious on top of each one. There's actually an entire science behind cheese varieties and the temperatures at which they best melt. The folks at FineCooking.com do a great job mapping it all out. I've found that when the cheese spends the entire baking time in the oven it goes beyond its melting point. By adding the cheese midway through the baking time, it spends less time exposed to the high heat needed to properly bake the puff pastry, and the result is the perfectly melted topping.