|Dark chocolate||6 3⁄4 Ounce (70% Cocoa Solids, 190 Gram, Best Quality)|
|Unsalted butter||4 Ounce, cut into small pieces (115 Gram)|
|Caster sugar||5 1⁄2 Tablespoon|
|Water||3 1⁄2 Fluid Ounce (100 Milliliter)|
|Dark rum||3 1⁄2 Fluid Ounce (100 Milliliter)|
|Sponge finger biscuits||25 (Boudoir Biscuits Or Ladyfingers)|
Beat the egg whites until they form stiff peaks, adding half the sugar about halfway through.
Then carefully incorporate the egg whites into the chocolate-and-egg mixture using a metal spoon.
Mix the water, rum and rest of the sugar in a basin, and dip the sponge fingers quickly, just sufficiently long enough for them to take on a colour.
Line the base and sides of a 16-cm / 6 1/4-inch charlotte mould with the sponge fingers, so that the rounded side of each biscuit faces outward.
Pour the chocolate mousse into the mould and cover with the remaining sponge fingers.
Chill in the refrigerator for 4 hours.
Remove the charlotte from the mould by turning out onto a serving plate.
If it refuses to move, dip the mould for a few seconds in a basin of hot water.
Decorate with chocolate shavings.