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 an electric mixer for about 4 to 5 minutes.
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.
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.
Add the flour, which you sifted with baking powder and salt, back onto the mixture in two or three stages.
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.