Mix the espresso powder with the hot cream until fully encorperated. Pour the mixture through a sieve into a bowl with butter and chopped chocolate. Let stand for one minute.
Whisk the mixture until smooth and glossy. If lumps remain after mixing it for ~3 minutes, place it in the microwave or over a bowl of hot boiling water to heat the mixture and melt the remaining chunks.
Using a hand mixer, whip the mixture until soft peaks form, about 5-10 minutes. Cover the bowl with plastic wrap and place in the refrigerator to cool.
When solidified, spoon out tablespoons and roll into balls. Roll in tempered chocolate, cocoa powder, or whatever you like!