Cut four 3-inch wide strips of parchment paper and line the inside of four 3-inch metal ring molds, creating a tall collar. Grease the inside lightly with oil and set aside on a plate.

In a spotlessly clean, dry bowl, beat egg whites and cream of tartar with an electric mixer on medium speed until frothy. Gradually add sugar, then increase speed to high and beat until stiff, glossy peaks form. Set aside.

In a separate bowl, whisk egg yolks, milk, and vanilla until pale and slightly thickened. Sift in cake flour and baking powder, then whisk until just smooth with no lumps.

Add one-third of the meringue to the yolk mixture and whisk to lighten. Gently fold in the remaining meringue in two additions, using a spatula and cutting down the middle then up the sides until no white streaks remain. Do not deflate.

Heat a large non-stick skillet over the lowest heat. Grease lightly with oil and place the prepared rings into the skillet. Fill each ring almost to the top with batter. Add 1 tablespoon of water to the empty spaces in the skillet (not on the pancakes), then immediately cover with a lid.

Cook for 7–8 minutes. Carefully lift the lid, and using a spatula, gently flip the entire ring with the pancake inside. Add another 1 tablespoon water, cover, and cook for another 6–7 minutes until a toothpick inserted comes out clean or the center springs back.

Turn off heat, carefully remove the rings and peel away the parchment. Transfer pancakes to plates, stack them, top with a pat of butter, pour warm maple syrup over, and dust with powdered sugar. Serve immediately.