In the bowl of an electric mixer fitted with a whisk, whip the egg whites on medium speed until frothy, about 30 seconds. While continuing to whip, add one-third of the granulated sugar. Whip for 30 more seconds, add the remaining granulated sugar, and continue whipping until they reach soft peaks. With a rubber spatula, fold in the powdered sugar in 3 additions until well combined. Fold in the raspberry puree until no streaks remain. With a circular flat plastic stencil slightly smaller than the diameter of the sundae or verrine glasses you will use and a small offset spatula, spread the mixture evenly onto the Silpat. Repeat to make 10 circles per tray. Bake for 3 hours, or until the meringues are crisp. While still warm, loosen the meringues from the Silpat with an offset spatula (this makes extra since they are fragile). Finish cooling, and store in an airtight container for up to 3 days.