2 cups all-purpose flour
3/4 cup unsweetened cocoa powder
1 teaspoon baking soda
1 teaspoon salt
1 cup unsalted butter, at room temperature
3/4 cup white sugar
3/4 cup brown sugar
2 teaspoons vanilla extract
2 tablespoons coffee-flavored liqueur
1 cup finely chopped toasted hazelnuts
1 cup semisweet chocolate chips
1 cup milk chocolate chips
1 cup white chocolate chips
Preheat an oven to 375 degrees F (190 degrees C). Line baking sheets with parchment paper. In a bowl, mix the flour, cocoa, baking soda, and salt.
Beat the butter, white sugar, and brown sugar together in a bowl with an electric mixer until soft and creamy, then beat in the eggs, vanilla extract, and coffee liqueur. Gradually beat the flour mixture into the butter-sugar mixture until well combined. Stir in the hazelnuts, semisweet chocolate chips, milk chocolate chips, and white chocolate chips until evenly distributed through the dough. Drop by rounded teaspoons, about 2 inches apart, onto the prepared baking sheets.
Bake in the preheated oven until the edges are slightly browned, 8 to 10 minutes. Allow the cookies to cool on the baking sheet for 1 minute before removing to a wire rack to cool completely.