Preheat a medium size skillet with cooking oil on medium heat. Saute the onion and scallion for about 1 minute. Add salt and sugar and continue to cook on medium heat until the onions and scallion are wilted and really soft, probably around 15 minutes or so. Set aside. This can be prepared few days before
Making the cloud bread:
Preheat your oven at 300 F. Line a large baking sheet with parchment paper. Place 3 egg yolks and yogurt in a large mixing bowl. Stir to mix until smooth. Set aside. In another mixing bowl, whip the egg whites until they started to foam. Add cream of tartar and continue to beat until the egg whites are stiff. Even if you flip it upside down, it won't drop, that's when you know it's done whipping
Fold in 1/3 of the egg white into the egg yolk mixture. Use a rubber spatula to slice down and then scoop the bottom and fold over. Continue to do this motion until the egg white is just about mixed in and continue with the another 1/3 and so on. This way of folding is to ensure you do not lose too much air that makes this cloud bread so airy and fluffy
Use a spoon to scoop this batter into the baking sheet and use the back of the spoon to spread it out a bit (as shown in the video). Repeat with the rest of the batter. Top with the caramelized onion and scallion on top
Pop this into the oven, 3rd rack from the top and back for 30 minutes. It should be slightly golden brown at the end of cooking time. Let them cool down on the baking sheet for 5 minutes and then transfer to cooling rack to let them cool down completely