Coarsely chop both chocolates and set aside. Heat the cream and instant coffee in a large saucepan, stirring to blend. When bubbles start to form along the edge of the pan, remove from heat. Scatter the chocolate over the cream, stirring gently until melted. Set aside for 8 to 10 minutes. Add the liqueur and vanilla. Stir gently, just until evenly blended. Scrape the chocolate into a shallow bowl. Cool on a rack for 15 minutes, then cover the bowl with plastic wrap and refrigerate until firm, at least 4 hours or up to 1 week. Using a teaspoon or a melon baller, scoop up enough chocolate to make balls 1 inch in diameter. Place the balls on a parchment-lined baking sheet. Refrigerate for 15 minutes. Roll the balls in the cocoa, shaking off the excess, then transfer to wax paper until ready to serve. Best when served at room temperature.