Preheat oven to 200°C (approximately 400°F). Cook pudding with 400 ml (approximately 1 2/3 cups) milk as directed, let cool.
For the cake: Separate eggs and beat egg whites until stiff. Beat egg yolks with sugar until fluffy, mix in flour and salt and fold in egg whites. Line a baking sheet with parchment paper and pour batter into sheet. Bake for 10 minutes, remove and allow to cool.
For the filling: Whip cream until stiff, fold into prepared pudding. Using a cookie cutter, cut cake into heart shapes. Starting with cake, layer custard and cake three times, topping with custard. Put remaining cream in a piping bag and decorate, as desired. Chill to set and serve.