Begin by placing all the fruits, the butter, water and condensed milk in a saucepan, then simply bring it to the boil, stirring quite frequently to prevent it sticking.
Let the mixture simmer for 3 minutes exactly – still stirring occasionally and, whatever you do, don’t forget it! Now transfer the mixture to a large mixing bowl, to cool off for about 30 minutes. While it’s cooling, weigh out the flours, then sift them onto a plate, adding the salt and bicarbonate of soda. (When you sieve wholemeal flour there are usually some bits of bran left in the sieve, so just tip them back into the rest of the sieved flour.) When the fruit mixture has cooled, stir the flour, salt and bicarbonate of soda into it, adding a nice round tablespoon of marmalade too.
Then spoon the mixture into the prepared tin, level it off with the back of a tablespoon and bake the cake on a lower shelf so that the top of the tin is aligned with the centre of the oven for 1 hour and 50 minutes. Have a look halfway through, and if the top of the cake looks a bit dark put a double square of baking parchment on top to protect it. Then let the cake cool in the tin for 5 minutes before turning it out to cool on a wire tray.
When the cake is completely cold, gently heat the marmalade in a small saucepan with the water. Then brush it all over the top of the cake. Store in an airtight tin.
Pre-heat the oven to 170C, gas mark 3
You will need a Delia Online 20cm Round Loose-based Cake Tin (or similar), base and side lined