Preheat the oven to 350 degrees F. Line baking sheets with parchment paper and set aside.

Place the bittersweet and unsweetened chocolate and espresso powder in a medium bowl and place over a pot of simmering water and melt, whisking occasionally, until smooth. Sift together the flour, baking powder and salt onto a piece of parchment or wax paper, or into a small bowl, and set aside.

In the bowl of an electric mixer fitted with the paddle attachment, beat the butter, granulated sugar and light brown sugar until lightly and fluffy, about 2 minutes. Add the eggs, one at a time, then the vanilla extract, and beat on high speed for 1 minute. On low speed beat in the melted chocolate mixture until just combined. Fold in the flour mixture with a rubber spatula until just combined. Stir in the pecans and chips. The batter will be loose. Cover and refrigerate until just firm, about 30 minutes.

Using a small ice cream scoop (about 1 tablespoon size), scoop heaping tablespoons of the batter onto the prepared baking sheets, putting 8 cookies on each sheet. Bake for 10 to 11 minutes. The surface will be dry and shiny but the tops and insides will still be soft. It will take no longer than 10 to 11 minutes so set the time. Cool on the baking sheets for 2 minutes, then remove to a rack to cool 5 minutes longer. Repeat with the remaining batter. These cookies are best eaten the day they are made. Wrap leftovers well in plastic wrap and store in an airtight container.