Soak the dried cranberries in the whiskey for 15 minutes.
Melt the butter in a mug in a microwave for 20 seconds (800 watts). Pour the melted butter into a large bowl, then one by one, beat in the brown sugar, mixed spice, eggs, cocoa powder, flour, milk and half of the cranberries.
Divide the batter between four mugs. Top with the remaining cranberries.
Microwave each mug separately for 1 1/2 to 2 1/2 minutes each, until risen and firm. Serve immediately with eggnog ice cream (see our eggnog ice cream recipe).