I was lucky enough to be given a jar of home made marmalade by a friend - proper, chunky, dark, slightly bitter Seville marmalade. In a moment of need the other week I stole a proportion of the jam (leaving the peel) for the filling in a chocolate orange cake (4-egg sponge with 3tbsp cocoa + microplaned orange zest). This left me with marmalade too chunky to spread on toast, but I had another use in mind - tea bread.
Original recipe (Nigella forums)
8oz self-raising flour
4oz sugar (I used brown)
8oz mixed fruit soaked in 1 cup cold black tea
2 tbsp marmalade
It's possible to reduce the sugar and put more marmalade in (last time I made it I forgot the sugar entirely, oops, and it was perfectly edible). I soak my fruit for a good 3hrs or more so it's really plump, and I've found a combination of 5-6oz traditional mixed dried fruit plus 2-3oz cranberries works really well.
When it came to cake-making I mixed the marmalade and my beaten egg into the fruit/tea, then poured the wet mix over the sifted flour and stirred well. You can add a bit of mixed spice if you like.
In a loaf tin, it takes an hour at 170°C (fan) to cook to a nice moist-but-done consistency. Perfect sliced and spread with butter! The same mix makes 12 muffins, but make sure the pan is well greased and floured. Possibly about 20-25 mins for muffins to cook but I forgot to time it - just use the skewer test!