Place cashews in a bowl, cover with water, and let soak at least 2 hours; drain.
Blend cashews with ¼ cup water, whiskey, and 1 tbsp maple syrup until smooth.
In a greased, large coffee mug, stir egg, yogurt, 2 tsp maple syrup, and espresso powder. Add flour, cocoa powder, cinnamon, baking soda, and salt and stir until everything is moist.
Cover mug with a paper towel and microwave on high until puffed and set (between 90 seconds and 2 minutes).
Top with some whiskey-cashew cream. Save extra cream for more cakes, or stir into oatmeal.