Toast and chop the hazelnuts

• Spread the hazelnuts on a tray and toast until fragrant.
• Let them cool, then chop them coarsely.

Cream the butter and sugar

• Beat the softened butter with the icing sugar until pale and fluffy.
• Beat in the egg yolk and vanilla extract.

Make the dough

• Mix the flour, cocoa powder, cornflour, baking powder and salt.
• Add the dry ingredients to the butter mixture and mix to a soft dough.
• Fold in the chopped hazelnuts and chocolate chips.

Chill the dough

• Shape the dough into a disc, wrap it and chill until firm.

Shape the cookies

• Preheat the oven to 170 °C.
• Roll small balls of dough and place them on a lined baking tray, leaving space between them.

Bake

• Bake until set at the edges and slightly soft in the centre.
• Cool on the tray for a few minutes, then transfer to a rack.