Beat the egg yolks with the sugar until frothy and white. Add the flour while continuing to stir, followed by the grated lemon zest.
Bring the milk to the boil, add the egg mixture and place over the heat, stirring continuously until the custard thickens. Remove from the heat and cover with cling film.
Once the custard is cold, divide it between 4 bowls and add Fabbri Fruttinsieme to taste.