In a large mixing bowl sift together flour and icing sugar. Add butter and rub in until mixture is crumbly.
Preheat oven to 350℉
Press evenly into bottom and up sides of 9 inch flan pan with removable bottom. Dock the dough by pricking with a fork in several places. Bake at 350℉ for 18 minutes, or until lightly browned. Cool completely before filling.
Filling
While tart shell is cooling combine raspberries, 1/2 cup of the granulated sugar and cornstarch in a saucepan, stirring and cooking over medium low heat until sugar dissolves. Continue to cook until raspberries are tender. Cool to room temperature and then chill.
In a large bowl combine mascarpone chest, sour cream and remaining 1/4 cup sugar. Stir in grated lemon cyst.
Spoon cheese mixture into flan shell and alternately with half the raspberry sauce. Swirl gently with a knife to create rippled effect.
Chill for at least 1 hour before serving. Top with reserved raspberry sauce and a few fresh berries before serving..
Notes
Serve with a dollop of whipped cream.Store leftovers, covered, in the refrigerator for up to 3 days.