Meanwhile, for raspberry sauce: Place half of the raspberries and their juices in a medium bowl. Mash berries with a potato masher. In a small saucepan, combine sugar, cornstarch, and the remaining 1/2 teaspoon lemon peel. Add mashed raspberries. Cook and stir until thickened and bubbly; cook and stir for 2 minutes more. Remove from heat. Cool about 10 minutes. Stir in remaining half of the raspberries and their juices.