Step 1Heat the oven to 375 degrees.
Step 2Cream the butter and brown sugar in the bowl of an electric mixer until light and fluffy; scrape down the sides of the bowl often. Beat in the espresso powder, then the egg, then the Kahlua. Combine the flour, baking powder, baking soda and salt in a bowl and whisk to blend. Gradually beat into the batter. Stir in the chocolate chips and pecans.
Step 3Drop the dough by well-rounded teaspoons onto ungreased baking sheets. Bake until firm around the edges, 8 to 10 minutes. (Do not overbake.) Let stand 2 minutes, then transfer to wire racks to cool.