Step 3:
Add the oil, egg yolks, water, vanilla extract, and lemon zest (if using) to the dry ingredients. Beat well until smooth.
Step 4:
In another clean, dry bowl, beat the egg whites with the cream of tartar until frothy. Then, gradually add the sugar, continuing to beat until stiff peaks form.
Step 5:
Using gentle, compact movements, fold the beaten egg whites into the egg yolk and flour mixture. Be careful not to overmix, to keep the mixture light and fluffy.
Step 6:
Pour the batter into a springform pan (preferably ungreased) and spread it evenly over the surface.
Step 7:
Bake in the preheated oven for about 40-45 minutes, or until a toothpick inserted into the center of the cake comes out clean.
Step 8:
After baking, remove the cake from the oven and let it cool upside down. This helps maintain its moist texture.
