Preheat your oven to 180°C. Pour a teaspoon of vinegar into your mixing bowl and wipe it out with a cloth. Add the egg whites, sugar, and salt and let it whip for 5 minutes. Meanwhile, sift the almond flour, flour, and powdered sugar.
Line 2 baking sheets with parchment paper, fill a piping bag with a round nozzle and pipe tubes of about 6 to 7 cm nicely next to each other, optionally draw the bands of 6 cm on the bottom of your parchment paper with a marker, then you can pipe nicely in between. Sprinkle them with almond flakes and bake for 14 to 17 minutes. Remove them and let cool.
Mix the instant coffee with the hot water until well dissolved, let cool. Whip the mocha for 1 minute into the vanilla buttercream and put it in a piping bag with a serrated nozzle.
Detach the cookies from the parchment paper and pipe the buttercream filling on half of them. Place another cookie on top and let it set in the refrigerator for at least 1 hour. Once set, dip both ends in the melted chocolate and place them back on a plate with parchment paper to set again.
Can be stored in the refrigerator for up to a week, but they will be gone much faster than that 😉