Preheat the oven to 180℃ (160℃ fan)/350°F/gas mark 4. Lightly grease a 20cm (8in) shallow round cake tin.
Melt 50g (2oz) butter and 50g(2oz) caster sugar in a saucepan stirring until combined. Pour into the base of the prepared tin.
Finely grate the zest from two clementines and set aside. Peel and cut all 6 clementines in half across the segments. Remove any pips then arrange cut side down in the base of the cake tin. Scatter the cranberries into the tin around the clementines.
Place the remaining 125g (4oz) soft butter and 125g (4oz)sugar into a bowl and beat together until very pale and fluffy. Add the grated zest and beat again to combine. Gradually add 2 beaten eggs a little at a time, beating well after each addition. Then beat in 1 tablespoon milk.
Sift 125g (4oz) flour into the mixture. Use a spatula or large metal spoon to fold this in gently. You should have a nice dropping consistency – add a further tablespoon of milk if necessary.
Carefully spoon the prepared batter over the arranged fruit, spreading out gently to level.
Bake the cake tin in the centre of the oven for about 40 – 45 minutes until a cake skewer inserted in the centre comes out clean. Once baked, remove from the oven and place onto a cooling rack.
Allow the cake to cool for 5 minutes before turning out from the tin.