Sauté the onions in the butter. Add the meat and stir so that all of the pieces brown. Pour in the tomato puree, 1 ½ cup of water and salt, pepper and sugar and cook over a medium heat until it is tender and has some sauce left.
Grate the cheeses coarsely on a box grater. In the meantime, prepare the aubergine puree as follows: grill the aubergines whole over charcoal or over an open flame. Heat the butter in a pot and add flour. Mix well. Pour in the milk and continue to stir so that the mixture does not form lumps. When the sauce has thickened, add salt, pepper and nutmeg. Remove from the heat and add cream (optional) and continue to stir.