Put the cold butter and sugar in a mixer and blend for a few seconds until you get coarse crumbs.

Add the egg and blend for a few seconds.

Add the flour, baking powder and lemon zest and blend until incorporated.

Knead into a ball, flatten it, wrap it in cling wrap and refrigerate for 1 hour.

Roll the dough into a 3 mm - 1/8 ″ thick sheet.

Cut out 40 discs. Put some white chocolate on half of the discs and cover them with the remaining discs. Top with the crushed hazelnuts.

Bake in a pre-heated oven at 180°C – 355°F for 20 minutes or until golden.

Let them cool down on a wire rack and enjoy.