Preheat oven to 400 °F (200 °C).

Beat the egg yolks with sugar and vanilla sugar until creamy.

Add the lemon juice, lemon zest, and hazelnuts and knead together well.

Roll the dough out on a work surface dusted with confectioner’s sugar, cut out small hearts, and lay them on a buttered baking sheet.

Bake for 8–10 minutes, until golden.

For the glaze, sift the confectioner’s sugar and mix with the lemon juice.

Sprinkle the baked lemon hearts with the lemon glaze and let dry.