Melt bittersweet chocolate in top of double boiler over hot water.
In a medium mixing bowl, beat butter, sugar and brown sugar together on medium-high speed until light and fluffy.
Turn mixer down to lowest speed.
Add eggs and vanilla. Beat until combined.
In separate bowl, sift together flour, baking powder, baking soda, salt and espresso powder.
Add 1/2 flour mixture to creamed butter, mixing well.
Add 1/2 melted chocolate. Mix until ingredients are well-blended.
Add remaining flour, mixing completely.
Add remaining chocolate, again, yes, mixing completely.
Stir in chocolate chips and pecans.
Cover and refrigerate dough for 1 hour.
Preheat oven to 350°F.
Drop 2 tablespoonful of dough per cookie onto non-stick cookie sheet.
Place in preheated oven. Bake 15 minutes. (Adjust baking time accordingly for smaller cookies.)
Remove cookies to wire rack.
Store in airtight container at room temperature or in freezer for longer storage.