This is yet another Nigella recipe (but without glazing). You can get the 'proper recipe' in her (wonderful) website. My 7 years old son cannot get enough of this. My 9 years old son would not even try it, though he enjoys making it.
250 gr soft unsalted butter
75 gr caster sugar and 75 gr light brown sugar ( though 150 gr of any would do too)
150 gr marmalade
225 gr plain flour
half tsp bicarbonate soda
1 tsp baking powder
1 orange: zest and juice
Put all the ingredients in a food processor and mix them well. Pour over an oven dish or tin (previously buttered). Cook for 1 hour with a preheated over at 180 degrees (the original recipe calls for 40 minutes but it always takes us at least 20 minutes longer) until the whole mixture is set. Let it cool down and eat while it is still warm.