Place a metal bowl over a saucepan of barely simmering water and add the first three ingredients. Cook over low heat, stirring, until they are almost melted, then remove from heat. Continue to stir until they have all melted and the mixture is smooth. Mix together the flour, baking powder and salt in a small bowl. In another large bowl, beat together the eggs and sugar, using a mixer, for approximately 10 minutes. Add the espresso power if using (I like these better without), also the vanilla, and beat for 2 additional minutes. Stir in the melted chocolate until it is evenly mixed, then add the flour/baking powder/salt mixture. When that is smooth, fold in the chocolate chips. Refrigerate the batter for 20-25 minutes. Meanwhile, preheat the oven to 350degreesF. Line your cookie sheets with parchment paper. Drop chilled batter by heaping tablespoonfuls onto the parchment lined cookie sheets about 2-inches apart. Bake cookies, one baking sheet at a time, for approximately 8-10 minutes. When done, cookies may appear cracked and shiny on top. Allow cookies to rest for a few minutes, the place on a cookie rack to complete cooling. Store any cooking you are not eating right away in the freezer or refrigerator, not the cookie jar.