6 tablespoons (3/4 stick) unsalted margarine or butter
12 ounces semisweet chocolate chips, divided
2 ounces unsweetened chocolate
2 extra-large eggs
1 tablespoon instant espresso powder, such as Medaglia d’Oro
2 teaspoons pure vanilla extract
3/4 cup sugar
1/3 cup plus 1 tablespoon all-purpose flour
1 teaspoon baking powder
1/4 teaspoon kosher salt
1 cup whole walnuts in large chunks
1 cup whole pecan in large chunks
2/3 cup peanut butter chips
Preheat the oven to 325 degrees F. Line two cookie sheets with parchment paper.
In a double boiler or over very low heat, in a medium saucepan, melt butter, 6 ounces of the chocolate chips, and the unsweetened chocolate, stirring occasionally, until just melted. Remove from the heat and cool for 15 minutes.
In an electric mixer, beat the eggs, espresso powder, and vanilla until combined. Add the sugar, raise the speed to medium-high, and beat for 2 minutes, until the batter is thicker.
With the mixer on low, slowly add the chocolate mixture to the egg mixture. Combine the 1/3 cup of flour, baking powder, and salt in a small bowl and fold it into the chocolate mixture with a rubber spatula. In another bowl, combine the walnuts, pecans, peanut butter chips, the remaining 6 ounces of chocolate chips, and the tablespoon of flour and fold it into the chocolate mixture. Drop by rounded mounds, about 2 tablespoons each of batter, 1 inch apart onto the prepared sheet pans. Bake for 15 minutes exactly. Cool on the baking sheets.