Place the butter in a microwave-safe mug that holds at least 10 ounces, and microwave on LOW until melted.

Stir in the crushed gingersnaps and press the mixture firmly into the bottom of the mug.

In a separate bowl, whisk together the pumpkin pur?e, egg, milk or cream, brown sugar, and pumpkin pie spice. Pour into the mug over the gingersnap 'crust'.

Microwave on full power for 2 to 5 minutes, checking for doneness with a knife; it should come out clean.

Let it cool for a couple of minutes; top with whipped cream and crushed nuts if desired.