Grease and base line a 30cm x 23cm (12inch x 9 inch) tin.
Preheat your oven to 180C /356F/ Gas 4.
Break your chocolate into pieces and put it with the butter into a heatproof bowl.
Place it over a pan of hot water and melt the chocolate slowly, stirring from time to time. Don’t let the bowl touch the water in the pan.
When the chocolate is melted remove from the heat.
In another bowl mix together the eggs, sugar and marmalade. Gradually beat in the chocolate mixture.
Fold in the flour.
Spoon the mixture into the prepared baking tray and bake in the preheated oven for about 40-45 minutes until firm on top and a dull crust has formed.
Leave to cool in the tin on a wire rack. When completely cool cut into squares