1. Preheat oven to 250°.
2. To prepare meringues, cover 2 baking sheets with parchment paper. Draw 4 (4-inch) circles on each piece of paper. Turn paper over; secure with masking tape.
3. Place cream of tartar and 4 egg whites in a large bowl; beat with a mixer at high speed until foamy. Gradually add 3/4 cup granulated sugar, 1 tablespoon at a time, beating until stiff peaks form.
4. Divide the egg white mixture evenly among 8 drawn circles on baking sheets. Shape meringues into nests with 1-inch sides using the back of a spoon. Sprinkle evenly with nuts.
5. Bake at 250° for 1 hour, rotating baking sheets after 30 minutes. Turn oven off, and cool meringue nests in closed oven for 2 hours. Remove from oven, and carefully remove meringue nests from paper.
6. To prepare lemon curd, combine whole eggs and 1 egg white in a medium bowl; stir well with a whisk. Heat 1/2 cup granulated sugar, rind, juice, potato starch, and salt over medium-high heat in a small, heavy saucepan to 180° or until tiny bubbles form around edge. Gradually add hot juice mixture to egg mixture, stirring constantly with a whisk. Return juice mixture to pan. Cook over medium heat for 2 minutes or until thick, stirring constantly. Spoon curd into a bowl; cool to room temperature. Cover and chill.
7. Arrange about 1/4 cup raspberries in each meringue nest; top with about 2 tablespoons lemon curd. Sprinkle the nests evenly with powdered sugar, if desired. Serve immediately.