• 175 g/6 oz butter
• 175 g/6 oz caster sugar
• 1 egg yolk
• 90 g/3 oz plain or bitter chocolate, melted
• 2 tablespoons dark rum
• 20–30 sponge finger biscuits

Mix the butter, sugar, egg yolk and melted chocolate to a smooth cream.

Almost fill a cup with cold water, add the rum and pour into a bowl. Dip the biscuits in the liquid, but do not saturate them. Place a layer of sponge fingers in an oblong tin (21×10 × 6 cm/8½ × 4 × 2½ in) lined with greaseproof paper. Follow this by a layer of the cream mixture. Continue to fill the tin alternately layering with sponge fingers and cream mixture until all is used up, ending with sponge biscuits. Place a lid on the tin and a weight on the top to hold it down. Refrigerate for 2–3 hours, before serving.