Butterscotch sauce

• 8 oz (225 g) granulated sugar
• 3 tablespoons water

Put the sugar into a dry saucepan and stir over moderate heat until the sugar has melted and turned to a light, golden caramel. Draw the pan off the heat at once (or caramel will become too dark) and allow the bubbles to subside. Put the water into a teacup and carefully add all at once to the sugar. (Take care: the mixture bubbles up on the addition of a liquid.)

Add the butter and sti