Work the flour, butter, powdered sugar, salt, vanilla pulp and lemon zest into a shortcrust pastry. Shape the dough into rolls with a diameter of 2 cm, wrap in foil and put in the fridge for about 1 hour.
Preheat the oven to 170 °.
Whisk an egg white and brush the rolls all around, turn in the granulated sugar and press down. Cut the rolls into 0.5 cm thick slices and place them 2 cm apart on a baking sheet lined with baking paper, bake for approx. 15 minutes and allow to cool.
In the meantime, mix the apricot jam with the lemon juice, heat, stirring constantly, and simmer for 2-3 minutes. Then spread the mixture on the not yet cooled down thalers and let dry.