01 -
Beat the softened butter, powdered sugar, and salt in a mixing bowl for 2-3 minutes, until pale and smooth.
02 -
Melt the dark and milk chocolate gently in 20-second microwave bursts, stirring between each burst, or use a bowl set over barely simmering water. Let it cool until warm but not hot.
03 -
Beat the melted chocolate into the butter mixture. Add the rum and cocoa powder, then mix until glossy and evenly combined.
04 -
Cover the bowl and refrigerate for 60-90 minutes, until the mixture is firm enough to scoop and roll.
05 -
Scoop teaspoon-size portions and roll into small balls with cool, dry hands. If the mixture softens, chill it again for 10-15 minutes.
06 -
Roll each ball in chocolate sprinkles or cocoa powder. Store in an airtight container in a cool place or in the refrigerator, and let the Rumkugeln rest several hours before serving.