Heat the butter, 4 ounces of the chocolate chips, and the unsweetened chocolate together in a medium heat-proof bowl set over simmering water just until the chocolate melts. Remove the bowl from the heat and allow to cool for 15 minutes. In a large bowl, stir (do not beat) together the eggs, coffee powder, vanilla, and sugar. Stir the chocolate mixture into the egg mixture and set aside to cool to room temperature.