Finely chop the shallot and garlic. Peel plantains and sweet potatoes and thinly slice them. Mix cream, crème fraîche, shallot pieces and garlic and season it with salt, pepper and nutmeg.
Bake plantains in their skins for 20 min. Mix cream with spices, salt and vanilla sugar and bring to the boil. Add grated couverture, finely purée with the hot plantain flesh, press through a sieve and chill for 8 hours. For a fluffier mousse, whip in the cream.
To make the béchamel sauce, melt the butter, add the flour and whisk over a low heat for 2 to 3 minutes. Add salt and pepper. Put the olive oil in a frying pan, brown the mince and season with salt and pepper.
Bread the plaintains using one or all of the various coatings in egg and then flour and deep-fry. Brown plantains are especially good with an egg coating, green and green-yellow ones with all other coatings. Green plantains can be deep-fried without any coating, but should be lightly salted afterwards.
Place tin of condensed milk in a pan and cover with water. Bring to the boil and simmer for 2 hours to caramelise the milk. Important: Keep topping up water to keep can covered at all times.