Allow egg whites to stand at room temperature for 30 minutes. Meanwhile, line a baking sheet with parchment paper or foil. Draw a 9-inch circle on the paper or foil. Invert paper or foil so the circle is on the reverse side.
Preheat oven to 250 degrees F. For meringue, in a large mixing bowl beat egg whites, salt, and cream of tartar with an electric mixer on medium speed until soft peaks form (tips curl). Add the 1 1/2 cups sugar, 1 tablespoon at a time, beating on high speed until stiff peaks form (tips stand straight). Beat in lemon juice and vanilla. Sift cornstarch over egg white mixture; using a rubber spatula, gently fold cornstarch into egg white mixture.
Spread meringue over circle on paper or foil, building up edges slightly to form a shell. Bake for 1 1/2 hours (do not open door). Turn off oven; let meringue dry in oven with door closed for 1 hour.
For filling, 20 minutes before serving, clean, hull, and slice the strawberries. Place strawberries in a large bowl. Toss berries with the 2 tablespoons sugar. Tear mint leaves; gently stir mint into strawberry mixture. Let stand for 20 minutes.
Meanwhile, in a large mixing bowl beat the whipping cream and creme fraiche with an electric mixer on medium speed (or beat with a whisk or rotary beater) until soft peaks form (tips curl).
Place meringue shell on a large platter. Spread the cream mixture into the meringue shell. Spoon the strawberry mixture over the cream mixture. Serve immediately.