Heat oven to 350ºF. Line two baking sheets with a silicon mat or parchment.

In a mixing bowl, beat the egg and sugar until pale and frothy. Mix in the chocolate hazelnut butter until fully incorporated. Stir in the nuts.

Refrigerate the cookie dough for at least 15 minutes.

Drop tablespoons of dough onto the baking sheets. Use a fork to gently press a crosshatch pattern onto the top of each cookie, slightly flattening it.

Bake 7-9 minutes, or until crisp around the edges, but still soft in the center. Remove from the oven and let cool completely before removing from the baking sheets.