Add the Nutella and egg to a mixing bowl and combine with a mixer. Add half the flour and mix on low until just incorporated.
Add the rest of the flour and mix on low until you don't see any more white bits — do not overmix. The dough will be very stiff.
Line a baking sheet with parchment paper or a silicone baking mat.
Use a 1 ounce scoop (or measure 2 tablespoons of the mixture) to make dough balls on the cookie sheet, about 2-inches apart.
Use a cup or glass to flatten the balls slightly.
Bake 8-10 min, until the edges are set, and the middle looks dry and is no longer sticky to the touch. Allow the cookies to cool for 5 min on the baking sheet, then move them to a rack to cool for at least 30 minutes before enjoying.