Preheat your oven to 180°C (356°F).
Grease and line a baking tray or cake pan with parchment paper.
In a large bowl, beat the eggs and sugar together using an electric mixer for 3-5 minutes, until the mixture doubles in volume, turns pale, and becomes aerated.
Mix in the vanilla essence and lemon/orange zest.
Slowly add the sunflower oil in a steady stream while mixing on low speed until fully incorporated.
In a separate bowl, sift together the flour, baking powder, and salt.
Gradually add the cornmeal and sifted flour mixture to the wet ingredients, mixing on medium speed after each addition.
Reduce the mixer speed to low and gently mix in the full-fat yogurt, ensuring everything is fully incorporated but not overmixed.
Pour the batter into the prepared baking tray, leveling the surface with a spatula.
Bake in the preheated oven for 40-45 minutes, or until a toothpick inserted into the center comes out clean.
If the cake browns too quickly, cover it loosely with foil during the last 10 minutes of baking.
Let the cake cool completely before slicing with a sharp knife.
Serve plain, dusted with powdered sugar, or with a spoonful of jam.