Mix the gelatine with 3 tablespoons of cold water and leave to swell for 10 minutes. Beat the egg yolks with the lemon juice, the warm water and the lemon zest until foamy. Gradually add the sugar and vanilla sugar and beat again until creamy. Heat the gelatin until it is liquid and add to the cream, stirring constantly. Then beat in the milk and chill the cream.
Beat the egg whites until stiff and fold in when the cream thickens.
