Combine the flour, baking powder, and salt in a medium bowl; set aside. With an electric mixer on medium-high speed, beat the Nutella, butter, and granulated sugar until light and fluffy, about 2 minutes. Add the eggs, vanilla, and espresso powder and mix until incorporated. Reduce the speed to low and alternate additions of flour mixture and milk, starting and ending with the flour, and mixing until just combined after each addition. Fold in ½ cup of the hazelnuts. Refrigerate the dough until firm, at least 2 hours and up to 24 hours.
Preheat oven to 375 degrees F. Line baking sheets with parchment paper. Place the remaining hazelnuts and the powdered sugar in two separate bowls. Using a medium cookie scoop (or about 2 tablespoonfuls), roll the dough into balls, roll in the hazelnuts, then roll in the powdered sugar. Place the balls 2 inches apart on the baking sheets. Bake until the edges are set and the middle still looks a tad soft, about 10 minutes. Cool for 5 minutes on the baking sheet, and then transfer to a wire rack to cool completely. Store cookies in an airtight container at room temperature.