Preheat the oven to 425°F. Lightly grease (or line with parchment) two baking sheets., Melt the butter in a microwave-safe bowl, add the sugar, and return to the microwave for 30 to 45 seconds, until the mixture is hot to the touch., Beat in the vanilla, baking powder, salt, espresso powder, and egg. Cool to lukewarm., Add the flour and chocolate chunks, stirring briefly, just until well-combined., Drop the dough by tablespoonfuls onto the prepared baking sheets., Bake the cookies for 9 minutes, until they're barely set. Remove them from the oven, and cool right on the pan., Store in a cookie jar for up to a week.