Preheat the oven to 180°C (350°F/Gas 4). Butter and flour a 35 × 24 cm (14 × 10 inch) dish. To make the sponge, whip the eggs and the sugar for about 10 minutes with electric beaters on high speed until they are very, very thick and creamy and have bulked up a lot. Add the sifted flour, the salt and vanilla and fold in gently. Scrape out every drop into your dish, swinging the dish from side to side so that the batter goes to the edges evenly. Bake for about 20 minutes, or until the top is golden brown and the cake is cooked through and feels spongy. Turn out the sponge onto a wooden board to cool, and halve it horizontally through the middle with a long bread knife. Set aside for now and wash the dish.
Put the almonds in a blender and pulse-chop for a bit until they are coarse chunks. Remove about 4 tablespoons of the coarser chunks and continue pulsing the rest until they are finely chopped. Lightly toast the 4 tablespoons of coarser nuts under the grill (broiler) or in a dry frying pan until they are lightly golden. Set aside for now.
Meanwhile, make the cream. Put most of the 2 litres (8 cups) of milk in a saucepan, keeping about half a cupful on one side, and bring just to the boil, them remove it from the heat for now. Whisk together the egg and sugar with electric beaters until fluffy. Put the half a cup of cold milk in a bowl and gradually add the cornflour, stirring until it is smooth and dissolved. Whisk the dissolved cornflour into the egg mix. Add a ladleful of the hot milk to the egg mixture, whisking quickly to prevent any curdling, and then add another ladleful. Incorporate all the egg mixture into the milk pan and put it back over gentle heat, whisking all the time, until it starts to thicken and make bubbles on the surface. The whisk will start to leave thick trails behind it, so let it bubble for a few minutes and then remove the pan from the heat. Stir in a tablespoon of rose water and the finely chopped almonds. Leave to cool a bit, whisking now and then. (The cream should look like a very pale, fairly loose custard and will thicken more as it cools, and then later in the fridge.)
Put one layer of sponge back into the clean glass dish. In a cup, mix together the 4 tablespoons of milk, the rose water and Cognac and dribble (or brush) about half of this evenly over the sponge layer. Cut up about four pieces of fruit in syrup and arrange these over the sponge. Drizzle about 2 tablespoons of the thick fruit syrup over the sponge, and then pour over about half of the cooled cream, spreading it gently to cover the sponge completely.
Put the second layer of sponge on top. Drizzle the rest of the milk, rose water and Cognac mixture over the sponge, scatter with another four pieces of chopped fruit and drizzle with 2 more tablespoons of syrup. Finally spread the rest of the cream over the sponge, so that it is almost flush with the top of the dish. Scatter with the toasted almonds and leave to cool. Once cooled, cover the dish and put into the fridge. Leave it for at least a couple of hours before serving.