Preheat oven to 350º F / 177º C
Line a baking sheet with parchment or a silicone baking sheet.
In a bowl, with a mixer, mix egg & hazelnut spread until mixture is glossy.
Add flour and beat until combined.
Cover bowl with plastic and let rest in fridge 10-15 minutes.
With a small cookie scoop, create dough balls (about 1.5 tbsp of dough) and place them on the cookie sheet.
If you are going to fill them, use your finger to press a dent into the top of each cookie. Filling is optional.
Mix the last 2 ingredients for the filling, and fill the dents.
Bake for 10 minutes. Take cookies out and allow to cool.