Combine the flour, baking powder, and salt, and sift them together.
Separate the yolks and whites of the eggs and put each in a separate bowl.
Separate ¼ of the sugar (for the whites) and the remaining ¾ (for the yolks).
Mix ¾ of the sugar, yolks, and vanilla together, and beat them with a mixer for about 4 to 5 minutes until they are completely white and creamy. Then set the yolks aside.
Clean and dry the beaters of the mixer. Beat the whites with an electric mixer for about 1 minute until they become foamy and white. Add the remaining ¼ sugar gradually to the whites while beating until the whites become slightly firm. Do not beat the whites for more than 2 minutes in total. Set the whites aside.
Now add the liquid oil to the yolks that were inside a separate bowl.
While the mixer is still on, add the orange juice to it.
Add the grated orange zest.
At this stage, add the beaten whites to the yolks. Fold the whites into the yolks gently with a spatula or a hand mixer (whisk/hand whisk); folding means to bring the whites up gently from the bottom of the bowl and mix them with the yolks; so that the volume of the whites does not deflate.
Add the flour, which you sifted with baking powder and salt, back onto the mixture in two or three stages. Our goal is for the flour to open up if it has clumped together.
Batter in the end
Place a 20 cm round cake pan with parchment paper on the bottom. Pour the prepared mixture into the pan. Bake in a preheated oven at 180 degrees Celsius for 40 to 50 minutes.
After 40 minutes, do a baking test. If it is not done yet, leave it for another 10 minutes.