• In a large bowl, beat the hazelnut spread and butter together until combined.
• Beat in the sugar, then the eggs, beating until smooth.
• Fold in the flour, baking powder, and salt.
• Cover and refrigerate for 30 minutes.
• Preheat oven to 350℉ and line baking sheets with parchment paper or silicone mat.
• Scoop the cookie dough onto the prepared pan.
• Bake in preheated oven for 12-15 minutes, depending on the size of your cookies. They should be just baked in the centre and may still look slightly wet.
• Allow cookies to cool for 2-3 minutes on the pan before transferring to a wire rack to cool completely.

Filling

• Beat the butter and hazelnut spread together until smooth.
• Add the sugar, ½ cup at a time, beating to combine the sugar.
• Once cookies are cooled, spread a layer of filling on the bottom of half of the cookies. Top each one with the remaining cookies to form a sandwich.
• Sprinkle a light dusting of icing sugar over the cookies before serving, if desired.