Filled meringues are a lovely finale to a Passover seder. Make components ahead, and assemble at the last minute. If serving on an occasion other than Passover, try adding one teaspoon vanilla extract to the meringues.
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.
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.
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.
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.
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.
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.