In a large microwave-safe mug, combine the spice cake mix, pumpkin puree, water, oil, and pumpkin pie spice.

Stir with a spoon or small whisk until no dry pockets of cake mix remain.

Place the mug in the microwave and cook on high for 60 seconds. The cake should rise and look set on top.

Lightly touch the center; it should spring back. If it still looks wet, microwave for an additional 10–15 seconds.

Let the mug cake sit for 1–2 minutes before eating. It will be very hot.

Enjoy as-is, or top with whipped cream, ice cream, or a sprinkle of cinnamon.