Step 1: In a medium bowl, whisk together the sifted cake flour, 2 tablespoons of granulated sugar, and baking powder. Set aside.
Step 2: In a separate large bowl, whisk the egg yolks with the buttermilk, vanilla extract, and melted butter until well combined and smooth.
Step 3: Gradually add the sifted dry ingredients to the yolk mixture, mixing gently just until combined. Be careful not to overmix; a few small lumps are acceptable.
Step 4: In a very clean, dry bowl (preferably metal or glass), add the cold egg whites. Using an electric mixer on medium-low speed, begin to whip the egg whites until foamy.
Step 5: Add the cream of tartar to the foamy egg whites. Gradually increase the mixer speed to medium-high. Once soft peaks form, slowly add the remaining 2 tablespoons of granulated sugar, one tablespoon at a time, continuing to whip.
Step 6: Continue whipping until the meringue holds stiff, glossy peaks. When you lift the beaters, the peaks should stand upright. Do not over-whip, as this can make the meringue grainy.
Step 7: Gently fold about a third of the stiff meringue into the yolk batter to lighten it. This makes it easier to incorporate the remaining meringue without deflating the batter too much.
Step 8: Add the remaining meringue to the batter. Using a spatula, gently fold it in using an upward, circular motion until just combined. The goal is to retain as much air as possible for fluffy pancakes.
Step 9: Lightly grease a non-stick pan and 2-3 individual soufflé ring molds (about 2.5-3 inches in diameter and 2 inches tall) with a little vegetable oil. Place the ring molds into the pan.
Step 10: Heat the pan over very low heat. Carefully spoon the soufflé pancake batter into each ring mold, filling them about three-quarters full.
Step 11: Pour about 1-2 tablespoons of water into the pan, around the molds (avoid pouring water directly into the batter). Immediately cover the pan with a tight-fitting lid to create steam.
Step 12: Cook for 5-7 minutes on one side, or until the tops of the pancakes look slightly set and puffed.
Step 13: Gently remove the lid. Using tongs, carefully flip each pancake within its mold (or remove the mold, flip, and then replace the mold around the flipped pancake). Add another tablespoon of water to the pan and cover again.
Step 14: Cook for another 5-7 minutes, or until cooked through and golden brown on both sides. The pancakes should be jiggly and light.
Step 15: Once cooked, carefully remove the pancakes from the molds and serve immediately with your desired toppings such as powdered sugar, maple syrup, or fresh berries.