Arrange the racks in the oven so that it separates the oven into thirds. Preheat the oven to 350°. Line two baking sheets with parchment paper and set aside.
Place pecans on a separate baking sheet and toast in the hot oven for 6-8 minutes until fragrant. Remove from oven and set aside.
In a small microwaveable bowl combine 8 ounces of the semisweet chocolate with the butter. Microwave in 10-20 second increments, stirring after each, until the chocolate and butter are melted and glossy. Do not over microwave. Set aside.
In a small bowl, combine the flour, baking powder and salt
In a large bowl, combine the eggs, sugar, espresso powder and vanilla. Using electric beaters on medium high, beat until thick and well combined, about 1-2 minutes.
Add the melted chocolate to the egg mixture and blend. Add the flour and mix until just combined. Roughly chop the toasted pecans and add them along with the white and dark chocolate chunks to the cookie mix. Stir to combine. Drop by heaping tablespoons, 2 inches apart, on the baking sheets.
Place one cookie sheet on the top rack and the other on the bottom rack. Bake for 6-7 minutes, then swap the cookie sheets so that the bottom moves to the top and vice versa. Bake another 5-6 minutes until cookies are just set. Remove from oven and let cool 2-3 minutes on the baking sheet. Use a metal spatula to transfer the cookies to a cooling rack. Cool completely before storing.