Preheat your oven to 350°F (175°C) and line two baking sheets with parchment paper.

In a large mixing bowl, cream together the softened unsalted butter and granulated sugar using an electric mixer on medium speed until light and fluffy, about 3–4 minutes.

Add in the vanilla extract, beating until combined.

Gradually sift in the all-purpose flour, cocoa powder, and salt into the creamed mixture. Mix on low speed until just combined.

Roll the dough into 1-inch balls and coat in finely chopped hazelnuts. Place on prepared baking sheets, spacing 2 inches apart.

Using the back of a rounded measuring spoon, create indentations in each dough ball.

Bake for 10–12 minutes, until edges are set but centers remain soft.

Let cookies rest for 5 minutes; if indentations have puffed up, re-press down gently.

Once cooled, fill each indentation with a generous dollop of chocolate hazelnut spread.

Allow to set slightly before serving.