Preheat the oven to 180 degrees C. Grease and line a 20 cm springform pan with grease-proof paper.
Bring the Cointreau and raisins to a light simmer in a saucepan, switch off the heat and keep aside to soak and cool.
Sift together the flour, baking powder and salt in a bowl.
In a separate bowl, cream the butter and sugar with an electric mixer till light and fluffy. Beat in the orange juice, rind and marmalade followed by the eggs one at a time.
Fold in the flour and then the raisins with the liqueur.
Pour into the springform pan and bake for 45 mins till the cake is done. Cool completely in the pan before turning out onto a plate.
Melt the chocolate gently in a double boiler and drizzle over the cooled cake.