Pour 2/3 of the milk in a pot, add the sugar and grated lemon rind, let them boil.
Stir the egg yolks well in a deep container with the remaining milk, vanilla and flour.
After the milk with sugar and lemon zest come to a boil, pour in the other egg and milk mixture in a thin trickle, while stirring nonstop.
Wait for the cream to thicken enough - then it's ready. In a suitable container, arrange in the following order, alternating: biscotti dipped in compote juice, then cream, biscotti... keep at it until out of ingredients.