Special equipment: a pastry bag fitted with the number 2 or number 3 tip, a paper cone or a plastic bag with the tip snipped off
Whisk together the confectioners' sugar, cocoa powder, vanilla, salt, instant coffee if using and 3 tablespoons water in a bowl until homogenized and there are no lumps.
Transfer the batter to a pastry bag fitted with the number 2 or number 3 tip, a paper cone or a plastic bag with the tip snipped off. Arrange 2 sheets of parchment paper on a clean surface and draw a series of long, thin parallel lines with the batter. Let dry at room temperature for 24 hours.
Cut the lines into sprinkles using a chef's knife. Sprinkles keep in a well-sealed container at room temperature for several months. Use them on top of ice cream, over truffles or even... on bread!