Put the eggs and sugar in a bowl and mix until smooth and homogeneous. Incorporate the rainmeal and, if the dough is too dry, add 3 tablespoons of cold milk. In a separate pot, boil the remaining milk with the peel of the lemon or orange and then turn off the fire. Incorporate the milk into the compound and mix gently taking care not to form lumps. Place the pot with the cream on the fire (low flame) and bring to the boil. Once the cream has thickened, move it into a glass container and let it cool before using it.