In a heatproof bowl, melt the butter until it’s almost but not fully melted.
Add the sugars and whisk for about 60 seconds.
Add the vanilla, salt and egg and whisk for another 60 seconds.
Pour in the hazelnut butter and whisk well.
Add the flour and baking soda and stir with a rubber spatula.
When it’s almost fully mixed, add the chocolate until it’s all mixed together.
Cover with a tea towel and set on the counter for an hour.
Preheat the oven to 350 F. Line two greased cookie sheets with parchment paper.
Scoop about 2 tablespoons of dough onto the prepared sheets, leaving a full one inch space border between cookies.
Bake until slightly browned around the edges and set in the center, about 12 minutes.