Add other leftover festive ingredients such as nuts or dried fruits. They can be cut into mini squares for nibbles or for dinner parties, top with ice cream and berries.
Preheat the oven to 180°C (350°F) mark 4.
Melt the butter and chocolate in a heavy pan over a low heat, stirring frequently until melted and smooth. Remove from heat.
Beat the sugar, with the eggs and cranberry sauce in a bowl and pour in the chocolate mixture with the vanilla extract, flour and salt.
Pour into a 21cm square tin and bake for 15-20 minutes. If you put in a toothpick it should come out wet.