For the mocha foam, whisk all ingredients until the powdered sugar and espresso powder have completely dissolved.
Pour into a 0.5 L iSi device, screw on an iSi cream capsule and shake vigorously. Chill in the refrigerator for 1-2 hours.
Mix fresh or frozen blackberries with 3 – 4 tbsp. granulated sugar and pour into a glass. Serve with the mocha foam and crumbled amarettini.