Start by preparing a square or rectangular mold with enough bottom for our spongy coca de llanda can rise (about 4-6 cm- 2, 35 inches high).
You can prepare the mold with baking spray, olive oil or parchment paper that can stand up from the sides of the mold, so it will be easier to unmold our coca.
Clean well the lemon peel we will need for the lemon zest and the 1/2 spoon of lemon juice (we will add 1/2 lemon juice if we bake with baking soda instead or gaseosillas).
Preheat the oven to 180º Celsius (355º Fahrenheit) with heat up and down.
In a bowl mix the eggs with the white sugar and the lemon zest with the help of a whisk or electric beaters (like KitchenAid) until they whiten and are perfectly integrated.
Add the olive oil, ½ teaspoon of lemon juice and the rum to the mixture of eggs and sugar and mix again with your whisk or electric mixer.
Then add the milk to the mixture and beat again.
Sift the flour and the baking soda that we will gradually add to the mixture of eggs, milk, oil and sugar and beat again.
Place your coca de llanda batter in the mold that we have previously prepared.
Mix in a bowl 3-4 tablespoons of white sugar and ½ teaspoon of cinnamon.
Sprinkle a generous layer of the sugar and cinnamon mixture over our coca de llanda batter.
Bake for 25-35 minutes depending on the oven, until the surface of our olive oil sponge cakeis golden brown, and a toothpick inserted in the center comes out dry.
Let cool and serve our spongy coca de llanda with its top layer of caramelized sugar and enjoy!