Preheat oven to 350 degrees and place rack in center of oven. Place the pecans on a baking sheet and bake for 8-10 minutes, or until lightly brown and fragrant. Let nuts cool and then chop coarsely.
whisk together the flour, baking powder, salt, and espresso powder. Melt the chocolate and butter in a stainless steel bowl placed over a saucepan of simmering water, stirring until smooth. Remove from heat and set aside to cool to room temperature
In the bowl of your electric mixer (or with a hand mixer), beat the sugar and eggs until pale yellow and thick, about 5 minutes. Beat in the melted chocolate mixture and vanilla extract. Fold in the dry ingredients to the chocolate batter and mix only until incorporated. Stir in the chocolate chips and nuts. Cover with plastic wrap and refrigerate the batter just until firm, about 30-60 minutes.
Preheat oven to 350 degrees and place rack in center of oven. Line two baking sheets with parchment paper.
Remove from oven and place baking pan on a wire rack to cool. When cookies are firm, remove from baking pan and let completely cool on rack.