Heat the oven to 180 C and prepare any suitable baking pan you like. Discard the white parts of the citrus peels and finely chop them as tiny as you can. You need about 25g of it.
Add the ricotta cheese, preserved lemon purée, salt, oil, sugar and egg with the chopped citrus zest into a bowl and whisk.
Sift the flour and both baking agents into the batter and whisk or fold carefully until well combined.
Transfer the dough-quality batter into the baking pan and sprinkle the top with sugar. Bake for 35-40 min. until golden on top and baked through. Let cool on a rack before serving.