Pound and sieve the sugar and beat with egg yolks until white. Shave ½* vershok vanilla bean with a knife, add the shaved vanilla and the cream to the sugar and egg yolks, and stir on top of the stove until the mixture thickens but do not let it boil. Strain and cool, stirring occasionally. Pour into a mold and proceed as indicated in the remarks. If using lemon zest, add it to the cream after it has cooled.