In a food processor combine hazelnuts, flour and sugar. Process at high speed for 30-60 seconds, until the hazelnuts resemble very fine crumbs or powder.

Transfer the mixture to a large bowl. Add the melted butter, egg, salt and vanilla. Stir with a wooden spoon and then use your hands to make a dough.

Refrigerate the dough for 30-60 minutes.

Preheat oven to 360º F/ 180º C. Line two large baking tins with sheets of parchment paper.

Use a 2 inch/ 5 cm round cookie cutter to make the cookies. Use a smaller cutter to make a whole inside half of the cookies (I used a heart shaped fondant cutter).

Bake for about 10 minutes or until the edges start becoming golden brown. Let the cookies cool and then sandwich them with the chocolate spread. Use a cookie without a hole for the bottom and one with a hole for the top.

Sprinkle with icing sugar before serving.