Millionaire's Shortbread Filling and Topping
1 14 ounce sweetened condensed milk
6 ounces semi-sweet or bittersweet chocolate, cut into pieces
1/2 teaspoon unsalted butter
Pour the condensed milk into a heatproof bowl and place the bowl over a saucepan of simmering water.
Cover and cook, over low heat, stirring occasionally, for 45 to 60 minutes or until the milk has thickened and has turned a light caramel colour.
Remove from heat and beat until smooth.
Pour the caramel over the baked shortbread and leave to set.
Melt the chocolate and butter either in the microwave oven or in double boiler.
Pour the melted chocolate evenly over the caramel and leave to set.
Cut the shortbread into pieces using a sharp knife.
Store the shortbread in the refrigerator to keep the chocolate firm.