2 tablespoons brewed espresso, or as needed
1 1/2 tablespoons water
1 1/2 tablespoons instant espresso powder
Stir sugar, espresso, water, and espresso powder together in a bowl with a fork until all the liquid is incorporated and the mixture has the consistency of wet sand. Pour mixture onto a baking sheet. Press sugar mixture by hand into a firmly-packed rectangle. Straighten the sides of the rectangle with a dough cutter or metal spatula. Cut mixture into small cubes and spread cubes slightly apart on the baking sheet. Dry cubes at room temperature until set, about 24 hours.