½ cup plain chocolate

½ stick butter

2 Tablespoons double cream

1 teaspoon vanilla extract

Melt the chocolate and butter in a bowl over a pan of simmering water or in the microwave.  Stir well and add the cream and vanilla.

Sift the powdered sugar into a mixing bowl and gradually beat in the chocolate mixture.  If the mixture is too stiff, add a little more cream.

Press into a shallow buttered tin and chill until firm.