Preheat the oven to 180°C (thermostat 6). Whisk the eggs with the sugar until pale. Zest the orange then squeeze the juice.
Add the flour, baking powder, orange juice and large citrus olive oil in turn. Finally add the orange zest and stir again. Butter the mold and pour the batter into it.
Bake for 30 to 40 minutes depending on the size of the mold chosen; test for doneness with a knife, the blade of which should come out clean. Leave to cool for 10 minutes out of the oven before unmolding.