Peel the onion and cut into small cubes. Fry in hot oil to get a golden colour. Put into a bowl and leave to cool down. Wash the tomatoes and cut them into quarters.
Sift the flours, baking powder, soda and salt into the bowl. Pour the milk and oil into the second bowl. Pour the eggs into the bowl and mix using a whisk. Pour the wet ingredients into the dry ones and add onion, tomatoes and basil. Mix with a spatula to achieve a homogeneous mass. Mix only until the ingredients are combined. Do not use a mixer! Fill the muffin mould with muffin cases. Use a spoon to put the mass up to 2/3 of the height of the muffin cases. Bake using thermaflow in 180° C (350° F) for approx. 20-25 minutes until obtaining the so-called “dry skewer stick”. Cool down on a cooling rack.