Place the unopened can of condensed milk
in a pan and cover with water, then bring to the boil, cover and
simmer for 3 hours, topping up with boiling water as necessary. The
milk will turn into a caramel. Leave to cool before opening.
Melt the granulated sugar in a heavy-based pan over a low heat until
melted and light golden. Remove from the heat and stir in the water,
being careful as it may spit. Stir until blended, then leave to cool.
Add the vanilla essence.
Cream together the butter or margarine and caster sugar until light
and fluffy. Gradually beat in the egg yolks, then fold in the flour,
baking powder and salt alternately with the sugar and water mixture.
Whisk the egg whites until stiff, then fold them into the mixture
using a metal spoon. Spoon into two greased and lined 23 cm/9 in cake
tins (pans) and bake in a preheated oven at 180°C/350°F/gas mark 4 for
30 minutes until golden brown and springy to the touch. Leave to cool,
then cut horizontally into three layers.
Remove the caramel from the can and beat until slightly soft. Sandwich
the cakes together with the caramel. Whip the cream until stiff, then
pile on to the top of the cake and sprinkle with grated chocolate or
chocolate curls. To make the curls, scrape a sharp knife down the edge
of a block of chocolate so that the mixture comes away in curls.