Preheat oven to 350°F. Line 2 cookie sheets with parchment paper; set aside.

Using a double boiler or a small heatproof bowl set over a pot of gently simmering of water, melt chocolate until smooth. Set chocolate aside to cool for 5-10 minutes.

Meanwhile, using a medium bowl, add flour, cocoa powder, baking powder and salt; stir until well combined. Set bowl aside.

Using an electric mixer, cream together sugar, brown sugar and butter for 2-3 minutes on medium speed. Add eggs and egg yolk; mix for 2-3 minutes, or until mixture is light pale in color. Add cooled chocolate and vanilla; mix until just combined. Finally, add dry ingredients, chocolate chips, white chocolate chips and pecans (optional); stir until just combined.

Roll 2 Tbsp of cookie dough into a ball and place on prepared cookie sheet. Gently flatten ball with palm of hand. Repeat with remaining dough, leaving 1½” in between cookies.

Bake 12-14 minutes, or until edges of cookies just begin to turn crispy. Let cool before removing from cookie sheets.