In a saucepan over medium heat, scald the milk. Add the lemon peel and remove from the heat. Let sit 1 hour. After 1 hour, strain the milk to remove the lemon peel.
In a bowl, beat the egg yolks until light and fluffy. In another bowl, combine the cornstarch, sugar and flour, add to the egg yolks and beat until light and fluffy, 1 minute.
Scald the milk a second time and add the milk slowly to the eggs, whisking constantly. Place the mixture back in the saucepan and over low heat, stirring, cook until the mixture thickens and bubbles around the edges. Remove from the heat and whisk in the vanilla, lemon juice and butter. Fold in the mascarpone.
Preheat the broiler.
Divide the custard mixture between 6 or 8 individual gratin or tartlet dishes, 5-inches diameter. Press the strawberries into the custard mixture. Sift the confectioner's sugar onto the top. Broil until the tops are golden brown, 1 to 2 minutes.