150 grams (2/3 cup) granulated sugar
125 grams (about 1 cup) all-purpose flour
100 ml (1/2 cup) orange juice
1 teaspoon baking powder
Preheat the oven to 180ºC (350ºF). Grease a round cake pan (20 x 7 centimeters (8 x 2 3/4 inches)) with margarine and dust with some flour.
Separate the yolks from the whites. Beat the egg whites until stiff peaks form and store in the fridge.
In an electric mixer, beat on medium speed the egg yolks together with the sugar and the orange zest until obtain a creamy and homogeneous mixture. Pour the orange juice and beat for 1 to 2 minutes to incorporate.
Reduce the mixer speed to low, add the flour mixed with the baking powder and beat until a homogeneous mixture. Finally, fold gently with a spatula the whipped egg whites.
Pour the mixture into the prepared pan and bake until it starts to gain color (just like on the picture) and in the middle is a little bit higher than the rest of the cake, about 25 to 30 minutes (the time depends on the oven).
Remove the cake from oven and unmold onto a plate. Let cool to room temperature and serve.