Preheat the oven to 350 degrees F. Line a baking sheet with parchment paper.
In a large bowl using an electric mixer, beat together the butter and sugar until light and fluffy. Add the egg, vanilla, and coffee powder and beat until incorporated. Add the flour, cocoa powder, and salt, beating until just combined. If the dough feels dry, add 1 tablespoon heavy cream.
Roll the dough into 2 teaspoon size balls and place 1 inch apart on the prepared baking sheet. Using the end of a wooden spoon or your thumb, press gently in the center of each to create an indentation.
Transfer to the oven and bake, rotating sheets halfway through, until cookies are just set, about 7-8 minutes. If the indentations lose their definition, gently press the centers in again. Cool slightly on baking sheet and then transfer cookies to wire racks, and let cool completely.
Meanwhile, in a microwave safe bowl, combine the chocolate and cream. Microwave on 30 second intervals until melted and smooth. Stir in the vanilla and coffee powder until dissolved. Spoon the ganache into the center of each cookie. Decorate as desired with sprinkles or edible gold leaf. Keep cookies stored in an airtight container for up to 1 week.