Frozen Lemon Mascarpone Meringue Sandwich

Name: Frozen Lemon Mascarpone Meringue Sandwich
Ingredients: 1.5 cups plain flour ( 225 gm ); ½ teaspoon baking powder; ¼ teaspoon bicarb; 150 gm unsalted butter ( 1 stick and tablsp); ¾ cup 165 gm castor sugar; Zest of 2 lemons; 50 ml lemon juice (1½ tabsp); Vanilla; 250 gm ( 8.8 oz or 1 container) mascarpone; Zest of 2 lemons ( very finely grated); 1 cup caster sugar ( granulated); Juice of 2 lemons; 250gm (8 fl oz) thickened ( whipping) cream.; 4 egg yolks; 2 egg whites; ¾ cup of sugar