Filling
Add the egg and the salt into a bowl, mix until combined, add the butter and the milk, mix it all together very well.
Add the flour through a sieve and mix until a smooth mixture is formed, add the baking powder and mix lightly until all ingredients combine.
Put ¼ of the mixture on a skillet and spread it out into a thinner layer at the bottom of the 20cm skillet, add the fillings - grated mozzarella and grated ham to taste - finally, add the rest of the mixture, spreading until it fully covers the filling.
Cook over very low heat for about 8 minutes, but cooking time may vary depending on the oven power. Keep an eye on it to prevent it from burning. Then flip to cook the other side, cook for 5 minutes always being careful not to burn, put it on a plate. Serve.