1. The sweet potatoes are steamed in advance. There are many varieties of sweet potatoes. Try to choose the sweet ones that are not dry and not soft in texture;
2. Peel off the thin outer skin and use a spoon to mash the sweet potatoes for later use;
3. The cake materials are ready: cake flour, granulated sugar for egg whites, milk, corn oil, eggs, cocoa powder;
4. Put the milk and corn oil into the basin together, and stir evenly with egg soak to form an oil-free state;
5. Sift the cake flour into the corn oil and milk melt;
6. Stir evenly with egg yolk; separate the egg white and egg yolk, put the egg white into an oil-free and water-free egg beater, and put the egg yolk directly into the batter;
7. Use egg yolks to break up the egg yolks, mix well with the batter, and form a smooth and smooth egg yolk paste, set aside for later use; if the room temperature is relatively dry, cover the lid to prevent the surface moisture from evaporating and drying out;
8. Take 2 spatula egg yolk paste, pour 3 grams of cocoa powder into it, mix well, this is used to make giraffe markings; at this time, the oven can be preheated to 160 degrees;
9. The egg whites are beaten at a medium speed with an electric whisk, and the fine sugar is added in 3 times. They are: when the color of the egg white is not visible after the thick bubble is beaten, when the egg white is finely foamed, when the fine foam is beaten and there are slightly obvious lines; After adding sugar at a time, beat at medium speed for 1 minute, then turn to low speed. This will make the egg white paste very delicate, stable, and not easy to defoam; lift the egg beater, the egg white paste is in the shape of a big hook;
10. Take a spatula and mix the protein paste and cocoa batter evenly;
11. Put it in a piping bag;
12. Randomly squeeze out irregular patterns on the baking pan covered with greased paper; then put it into the middle layer of the preheated oven, bake at 160°C for 2 minutes, and take it out to cool after 2 minutes;
13. Mix the egg batter when baking the markings: take 1/3 of the egg white batter into the egg yolk batter;
14. Pour the mixed egg yolk paste back into the egg white paste;
15. Use a spatula to stir from bottom to bottom or cut and mix evenly to form a delicate and shiny cake batter;
16. Pour the cake batter into the baking pan, scrape the surface with a scraper, lift the baking pan and shake it lightly;
17. Put it into the middle layer of the preheated oven and heat up and down at 160 degrees for 30 minutes;
18. After it is out of the oven, shake it a few times, drag the cake out of the baking tray, place it on the drying rack, and tear off the oil paper around to dissipate heat;
19. Turn it over after 3 minutes, and tear off the greased paper on the bottom;
20. Roll the cake slice from the bottom up a few times, and then loosen it into a cake slice. The purpose of this is to form a "memory" while it is hot, which will make it easier to roll it in the next step;
21. When the cake roll is warm, you can spread the mashed sweet potato evenly on the striped side down and the smooth side up, and put more mashed sweet potato near the lower part that becomes the core of the roll;
22. Roll it into a roll from the bottom down. You can cut both ends of the cake without cutting it off. Wrap tightly with greased paper and clamp both sides with sealing clips. It can be placed at room temperature or in the refrigerator for about 30 minutes before being cut into pieces.
Tips:1. Eggs are medium in size, weighing about 60 grams per shell;
2. Do not bake the cocoa batter for too long to prevent it from being baked too dry and not melted with the original batter and breaking;
3. It is not advisable to beat the meringue too hard, as it will crack the cake when it is rolled;
4. The baking temperature and time are adjusted according to the actual situation of the oven. High temperature and low temperature should not be used to prevent excessive evaporation of the water in the cake if the baking time is too long.
