1Heat oven to 350°F. In medium bowl, mix flour, butter, 1/3 cup powdered sugar and 1 tablespoon of the lemon peel, using pastry blender or crisscrossing 2 knives, until coarse crumbs form. Press mixture evenly on bottom of rectangular pan, 13x9x2 inches.
2Bake 20 to 25 minutes or until crust is dry and light golden brown. Cool completely, about 30 minutes.
3In chilled medium bowl, beat whipping cream, 3 tablespoons powdered sugar and remaining 1 tablespoon lemon peel with electric mixer on high speed until stiff peaks form. Gently stir in yogurt. Spoon over crust. Top with nectarines and blackberries. Serve immediately, or cover and refrigerate until serving.
4For serving pieces, cut into 5 rows by 4 rows. Store covered in refrigerator.