Separate the egg yolks and egg whites. Place the egg yolks in a large mixing bowl and the egg whites in the bowl of your mixer. Set aside the egg whites.
Add the powdered sugar to the egg yolks and whisk until creamy. Stir in the whole milk, then the flour and baking powder.
Start whipping the egg whites with the salt, starting on a medium speed and gradually increasing to high speed until you get stiff peaks.
Place a non-stick skillet with a lid on your stove and turn on low heat (as low as possible).
While the skillet is warming up, fold about 1/3 of the whipped egg whites into the rest of the pancake batter. When smooth, add the rest of the egg whites in two times. Try not to overwork the batter to avoid deflating the egg whites.
Generously grease your pastry rings (see note 1 for sizes) and skillet with cooking oil (see note 2). Place the rings in the pan and fill about half of the rings with the pancake batter. They will rise while cooking so be careful not to overfill them.
Directly place the lid back on the skillet and leave to cook for 4 minutes. Carefully remove the lid (there will be some steam), gently flip each pastry ring with a flat spatula then place the lid back on for another 3 minutes.
If the Soufflé Pancakes do not come out easily of the pastry rings, run a small sharp knife around the edges of the ring.
Repeat the process if required, making sure to re-grease the rings between each rounds.
Serve directly, warm.