Peel the lemons with a vegetable peeler while avoiding the white of the fruit.
Scald the milk in a medium sauce pan. Add the lemon peel and remove from the heat. Let cool for 1 hour. After 1 hour, strain the milk and discard the lemon peel.
In a bowl, beat the egg yolks until light and fluffy.
In another bowl combine the cornstarch, sugar and flour. Add this mixture to the egg yolks and beat until light and fluffy, about 1 minute.
Scald the milk a second time. Add the warm milk slowly to the egg mixture while whisking constantly. Cook the mixture over low heat, stirring constantly until the mixture thickens and bubbles forms around the edge of the pan.
Remove from the heat and whisk in the vanilla, lemon juice and butter. Fold in the mascarpone until well incorporated.
Preheat the broiler.
Divide the custard mixture among 6 ramekins (6 - 8 oz.). Press the berries into the custard mixture top with sifted confectioners' sugar.
Place in the broiler until the tops are golden brown, 1 - 2 minutes. Serve hot or at room temperature.