1. Prepare the required materials: 70 grams of flour, 1 cup of yogurt, 4 eggs, 40 grams of sugar, 2 tablespoons of cooking oil, and a few drops of white vinegar.

2. Prepare two clean, oil-free and water-free bowls, separate the egg whites and egg yolks in the eggs, and put them into two bowls respectively. There should be no trace of egg yolk in the egg whites.

3. Add one cup of yogurt, two tablespoons of oil, and about 20 grams of sugar to the bowl containing the egg yolks, and stir evenly. Then add flour and mix well (as long as there are no lumps).

4. Next, beat the egg whites. First add a few drops of vinegar to the egg whites. You can add sugar in three times. Use a whisk to beat in one direction and add one-third of the sugar when the first stage is rough. (If you need to beat the eggs manually, you can put the container in a basin of warm water at about 40 degrees for easy beating, and beating by hand requires a certain amount of endurance and physical strength.)

5. Beat the eggs with a whisk until fine. Add a small amount of sugar while soaking

6. When the foam is wet and foaming (the foam is very delicate) (lift the egg beater and the foam will form a sickle shape), add all the remaining sugar,

7. Beat until hard foam is reached (at this time the foam can form an upright triangular tip).

8. Add the beaten egg whites to the egg yolk paste in three batches, mix evenly using a cutting and mixing method (just like stir-frying up and down for stir-fry), and rotate the container while mixing (do not use circular motions). Stir it in the form of stirring, otherwise it will easily defoam).

9. Mix well, shake it a few times, cover it with plastic wrap (to prevent water vapor from entering), then put it in a steamer and steam it for about 20 to 30 minutes.

10. After steaming, turn it upside down and wait until it cools before cutting. It will taste better after it cools.