In a mug, whisk together first four dry ingredients.
Add liquid ingredients and whisk until smooth.
Microwave for 1 minute and 30 seconds (if still runny, add another 15–30 seconds). Set aside to cool for 2 minutes.
While waiting, use smallest side of a cheese grater to finely grate butterscotch chips into a small bowl.
Once cupcake has cooled, top with whipped cream, butterscotch shavings, nutmeg, and cinnamon.