Heat oven to
350F (175C). Grease an oblong cake pan, 13 x 9 x 2 inches (33 x 23 x 5cm).
Put 1/2 cup (125ml). sugar in heavy skillet. Set over moderate heat and
melt, stirring with a wooden spoon. Continue heating until sugar becomes a
dark brown syrup (let it get darker than a caramel color but don't let it
turn black or it will taste bitter). Stir in boiling water gradually (be
careful of steam). Remove from heat. This is the burnt sugar syrup. Beat
egg whites until stiff peaks form. Set aside. Beat butter, 1 1/2 cups
(375ml) sugar and egg yolks together until fluffy. Combine cold water,
cream, 3 tbsp of the burnt sugar syrup and vanilla.