In a large mixing bowl, combine all the ingredients for the cookie dough. Stir until everything is blended into a smooth mixture.

Form the dough into a ball, cover it with plastic wrap, and let it chill in the refrigerator for at least 1 hour, preferably overnight.

Preheat your oven to 170°C (340°F). Line your baking sheets with parchment paper.

Roll out the chilled dough to about 3 mm thick on a floured surface. Use a cookie cutter to cut out heart shapes. For half of the heart cookies, use a smaller cutter to create a little heart or hole in the center.

Place the cookie shapes on the prepared baking sheets and bake them in the preheated oven for about 10 minutes. They should look matte, and the edges will slightly brown.

Melt the dark chocolate and drizzle it over the cookies with holes. Sprinkle them with hazelnut crunch for that extra delightful touch.

For the remaining cookies, spread a generous layer of Nutella or hazelnut spread, and then top them with the decorated cookies to create delicious sandwich cookies.

Allow the cookies to dry for about 1 hour. Once they’re set, store them in an airtight container in a cool, dry place.