Place chopped chocolate and butter in a large heatproof bowl set over a saucepan with ½-inch of barely simmering water. Stir occasionally until completely melted and smooth.
Add eggs, sugar, espresso powder, vanilla and salt to chocolate mixture and whisk until smooth. Sift in flour and baking powder and stir until evenly combined. Fold in peanut butter chips.
Cover with plastic wrap and refrigerate for 1 hour, or until chilled and firm enough to hold its shape.
Preheat your oven to 350°F and line 2 large baking sheets with parchment paper.
Roll tablespoons of chilled dough into balls and place onto prepared baking trays, spacing them about 2 inches apart. Flatten dough balls to about ½-inch thickness and bake for 7-8 minutes, until tops look shiny (not wet) and they feel set around the edges but still a bit soft in the middle. Be careful not to over-bake. Transfer baking trays to a wire rack and let cookies cool on the tray.