1. Beat the separated egg yolks in a water- and oil-free bowl
2. Add water and corn oil and stir evenly
3. Sift in cake flour and stir into egg yolk paste
4. Take a small amount of egg batter and add a small amount of purple sweet potato powder
5. Stir well
6. Add 2 drops of white vinegar to the egg whites, add sugar in three times and beat with an electric whisk to a wet foaming state
7. Take a little egg white and add it to the purple sweet potato batter, mix well
8. Put the purple sweet potato batter into a piping bag and squeeze it into a baking tray lined with greased paper
9. Bake in the oven at 160 degrees for about 3 minutes, and take it out after setting
10. Pour the remaining egg whites into the egg yolk paste, chop up and down and stir evenly
11. Then pour it into the baking dish and smooth it out
12. Bake at 160 degrees for 60 minutes in the oven
13. The baked cake is rolled up while it is hot and placed in the refrigerator for 1 hour to set
14. Time to take it out, remove the grease paper
15. Cut into sections and eat
Tips:Set the baking temperature according to your own oven habits.
