Roll out the puff pastry on a sheet of baking paper into a 3 mm – 0.1 inch thick sheet.
Cut 4 circles of approximately the same size as your tart tins and put the dough in the greased tins. Press it down well and make sure you have dough at the sides as well.
Prick the dough with a fork and keep aside.
Put the hazelnuts in a food processor and blend them.
Use this cream to fill the tarts.
Cook the tarts in a pre-heated oven at 200°C – 390°F for about 15-18 minutes, or until golden brown and cooked through.