In the bowl of an electric mixer beat the eggs and the sugar for �20 4 to 6 minutes, or until the mixture is thick and pale, add melted chocolate, the butter, the vanilla, the espresso, the flour, the salt and the baking powder, and beat the mixture on �20 the lowest setting until it is combined well. Add the chocolate �20 chips and the walnuts and beat the dough until it is combined well. In a sheet of parchment paper, form the dough into a log, �20 10 cm in diameter, wrap it in wax paper, and chill it for 3 �20 hours, or until it is firm. Cut the log into 3 cm-thick rounds, arrange the rounds 5 cm� apart on baking sheets lined with parchment paper, and bake them �20 in batches in the middle of a preheated 180ºC oven for 15 minutes,� or until the tops are shiny and cracked slightly. (The cookies �20 will be very soft.) Transfer the baking sheets to racks and let �20 the cookies cool completely before removing them from the sheets.� (The cookies will firm up as they cool.) Makes about dozen cookies.�20 The Model Bakery, St. Helene, Napa Valley From Gourmet Magazine