Step 1: In a medium bowl, whisk together the egg yolks, milk, vanilla extract, and a pinch of salt until smooth. Sift in the cake flour and baking powder. Whisk gently until just combined, being careful not to overmix.
Step 2: In a separate, very clean, large bowl, add the egg whites and cream of tartar. Using an electric hand mixer or stand mixer with a whisk attachment, begin whisking on medium-low speed until the whites become foamy.
Step 3: Gradually add the granulated sugar, about a tablespoon at a time, while continuing to whisk on medium-high speed. Increase the speed to high and continue whisking until stiff, glossy peaks form. The meringue should be firm and hold its shape.
Step 4: Gently fold about one-third of the meringue into the egg yolk batter to lighten it. Once partially incorporated, add the remaining meringue and continue to fold very carefully until just combined, trying not to deflate the air.
Step 5: Heat a non-stick pan or griddle over very low heat. Lightly grease the pan with a tiny bit of oil or butter.
Step 6: Spoon generous dollops of the batter into the pan, forming tall, thick rounds (about 1.5 to 2 inches high). Leave plenty of space between each pancake.
Step 7: Add about 1 tablespoon of water to the pan, away from the pancakes, and immediately cover the pan with a lid. Cook for about 4-5 minutes on the first side.
Step 8: After 4-5 minutes, check the underside for a light golden color. Carefully add another small dollop of batter on top of each pancake to build more height, then gently flip them. Add another tablespoon of water to the pan, cover, and cook for another 4-5 minutes until golden brown and cooked through. They should be wonderfully jiggly.
Step 9: Remove the Cloud Like Japanese Soufflé Pancakes from the pan and serve immediately with your favorite toppings.