Step 1Heat the oven to 225 degrees. In the bowl of a stand mixer or in a large bowl with a hand-held mixer, beat the egg whites until frothy on medium speed, about 1 minute. Add the cream of tartar and continue to beat to soft peaks, a minute more. Gradually add the sugar and continue beating until stiff peaks form, an additional 3 to 5 minutes. Beat in the vanilla and lemon juice. Fold in the hazelnuts.
Step 2Use a 2 1/4 -inch ring to trace circles onto parchment paper on a baking sheet. Spoon about 1 tablespoon of the meringue onto the center of a circle, and spread evenly to the edges. Repeat with the remaining meringue.
Step 3As you finish spreading each tray of meringues place them in the oven to bake for 1 hour to set the meringues, then turn off the oven but leave the trays inside for an additional 2 hours to allow the meringues to dry out. Remove from the oven, and gently peel them off the parchment paper. Store, loosely covered and in a dry area, at room temperature, until needed. The meringues will keep for 2 days.
Step 4Just before serving, spoon a tablespoon of sherbet onto a hazelnut meringue and top with another meringue, gently pressing the meringues into the sherbet to form a sandwich. Dust the tops lightly with powdered sugar. Serve two meringue sandwiches per person.