Preheat oven to 350 degrees. Combine all ingredients in a large bowl and mix to combine. Liberally spray a mini muffin tin with non-stick spray and spoon mixture to the top of each cup. Bake for 15-20 minutes, or until the edges of the cups are golden brown. Let cool for at least 5 minutes before removing from the mini muffin tin.
To freeze: Place baked cups on a baking sheet then freeze until solid and transfer to a freezer bag. Microwave for 20-40 seconds depending on how many you're reheating.
For regular-sized muffin tins: Bake for 25-30 minutes (Note: I have not tested full-sized muffins myself, although several readers have left comments saying this works!)