Heat a large nonstick skillet over low heat and grease three 3-inch ring molds in the pan. Beat the egg whites with cream of tartar until frothy, gradually add the sugar, and whip to stiff glossy peaks.

In a separate bowl, whisk the egg yolks, milk, vanilla, and salt, then sift in the flour and baking powder and whisk until thick and smooth.

Stir one-third of the whipped whites into the yolk batter to lighten it, then fold in the remaining whites in two additions until no streaks remain.

Fill the rings with batter to just below the top. Add a teaspoon of water to the skillet away from the rings, cover, and cook on the lowest heat for 4 to 5 minutes per side, flipping carefully.

Run a thin spatula around each ring to release, lift the rings off, and plate the pancakes immediately. Dust with powdered sugar and serve with butter and maple syrup.