1. Allow egg whites to stand at room temperature for 30 minutes. Meanwhile, line a large baking sheet with parchment paper. Draw two 8-inch circles on the paper. Invert paper so the circles are on the reverse side.
2. Position rack in center of oven. Preheat oven to 250°F.
3. For meringue shells, in a large mixing bowl beat egg whites, vanilla and cream of tartar with an electric mixer on medium until soft peaks form (tips curl). Add 1½ cups sugar, 1 tablespoon at a time, beating on high until stiff peaks form (tips stand straight). Beat in lemon juice. Sift cornstarch over egg white mixture; fold in gently. Spread meringue over circles on paper; build up edges slightly to form shells.
4. Bake for 1 hour (do not open door). Turn oven off, let meringue stand in oven with door closed for 1 hour. As the shells cool, cracking may occur.*
5. Meanwhile, for strawberry sauce, place halved berries and ¼ cup sugar in a food processor. Cover and process until smooth. Chill at least 1 hour.
6. For lemon cream filling, in a medium bowl, stir together mascarpone and lemon curd until well blended. Set aside. In a medium mixing bowl, beat cream and 3 tablespoons sugar until soft peaks form. Gently fold whipped cream into lemon curd mixture until smooth and incorporated.
7. Carefully lift one meringue shell off paper and transfer to a serving plate. Spread with half of the lemon cream mixture. Stack second meringue shell on top; fill with remaining lemon cream filling. Top with fresh berries. Cover and chill for up to 1 hour before serving. Serve with strawberry sauce. If desired, garnish with lemon zest.

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*Note: Store unfilled meringue shells in airtight containers at room temperature for up to 2 days or in the freezer for up to 6 months.

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