- In a saucepan, off the heat, combine the sugar and cornstarch. Add the egg yolks and combine with a whisk. Stir in the milk and lemon zest.
- Bring to a boil over medium heat, stirring and scraping the bottom of the saucepan. Simmer for about 1 minute. Remove from the heat. Stir in the butter and lemon juice. Pour into a bowl. Cover with plastic wrap directly on the lemon cream. Let cool and refrigerate until the mixture has cooled, about 1 hour.
- In a bowl, whip the cream, sugar, and vanilla with an electric mixer until stiff peaks form. Set aside.
- In a 20-cm (8-inch) square serving dish, spread a third of the lemon cream. Cover with half of the crackers. Spread a third of the lemon cream and half of the whipped cream. Continue with the crackers and the remaining ingredients, finishing with the whipped cream. Refrigerate for 8 hours or overnight.