1lb puff pastry
1 1/4 cups milk
2 teaspoons lemon zest
3 egg yolks
4 tablespoons caster sugar
1/4 cup flour
1 egg white
2 cups heavy cream
1 tablespoon rum
1 tablespoon vanilla extract
3 tablespoons confectioners sugar

1 lb puff pastry 1 1/4 cups milk 2 teaspoons lemon zest 3 egg yolks 4 tablespoons caster sugar 1/4 cup flour 1 egg white 2 cup s heavy cream 1 tablespoon rum 1 tablespoon vanilla extract 3 tablespoons confectioners sugar

Remove the puff pastry from the refrigerator and leave it at room temperature for 20 minutes. roll out on a lightly floured work surface so it forms an oblong 12"x5" shape. Trim the edges neatly, and prick over with a fork. Cut into two rectangles, each 6"x15".
Place the pastry on a large baking sheet lined with parchment paper. Mark one rectangle into 3 10" squares, cutting no more than halfway through the pastry. Chill in the refrigerator for at least 30 minutes.
Meanwhile, start making the pastry cream. Pour the milk into a small, heavy pan, and add the lemon zest. Slowly bring to a boil, occasionally stirring. In a separate bowl, whisk together the egg yolks and 1 tablespoon fine sugar in a bowl until thick and pale. Sift the flour into the yolk mixture and stir.
Whisk the hot milk slowly into the egg and flour mixture. Once mixed, put the mixture back into the pan. Stir the custard on low heat until it's thickened, then pour into a small bowl and cover. Set aside until cool but not firmly set.
In a separate bowl, whisk the egg white until stiff and whisk in the remaining caster sugar. Whip 2/3 cup of the cream until thick. Stir the rum into the custard, then gently fold the egg white mixture into the custard followed by the whipped cream. Cover with was paper and chill for 30 minutes.
Preheat the oven to 425F. Dampen the baking sheets around the pastry with cold water. Bake for 25 minutes until nicely golden and light. Remove from oven and let cool.
Pour 1 1/4 cups of cream into a chilled bowl. Add the vanilla extract and sift over 1 tablespoon confectioner's sugar. Whip the remaining cream.
Place the unmarked pastry sheet at the bottom of a baking dish and spread the pastry cream over top, then the whipped cream on top of that. Add the marked pastry sheet on top and dust with the confectioners sugar. Cut the kremna rezina into squares. Store in the refrigerator.