Optional meringue from Food & Wine: Whisk together 4 egg whites and 2 Tbsp. granulated sugar in a bowl from a stand mixer over a saucepan of simmering water until just warm, 1-2 minutes. Transfer bowl to stand mixer with whisk attachment. Add 1/2 tsp. cream of tartar; beat on medium high speed until foamy. Gradually beat in 1/2 cup granulated sugar until whites are stiff and glossy (3 minutes). Spread meringue on potatoes using the back of a spoon. Broil or use a blow torch until meringue is golden.