Preheat your oven to 180°C.
Place a puff pastry on a flat baking sheet and prick it with a fork.
In a salad bowl, mix the hazelnut powder, the sugar, the 2 eggs + the white of the 3rd (keep the yolk for the gilding) and the soft butter. Finally add the lemon jam and mix.
Place the resulting frangipane on the pastry, leaving a border of about 2 centimeters. Place the bean on the frangipane.
Moisten the edge of the puff pastry with a little water (using a kitchen brush or your fingers), cover with the second puff pastry, and stick the edges together. You can form patterns by gluing the edges together, like in the photo below.
Make patterns on top and brush with egg yolk diluted with a little water. Make a small hole in the dough in the center of the top.
Bake for 30 minutes.