Preheat the oven to 180°C (fan oven 160°C), gas mark 4. Generously butter 8 x 175 - 200ml (6-7 fl oz) metal pudding basins.
Put the sugar and butter together in a large bowl and, with an electric whisk (mixer or hand-held), beat together until very light and fluffy.
Add all the remaining sponge ingredients and continue to whisk for a further 2-3 minutes until the mixture is very smooth and creamy.
Spoon this into the prepared basins and level the top. Cover each one with buttered foil, butter side down and with the edges sealed tightly around the top of the basins.
Put the basins in a large roasting tin and fill with enough boiling water to come halfway up the side of the basins. Steam in the preheated oven for about 1 -1.25 hours.
Meanwhile, make the syrup. Put the compote, golden syrup and orange juice in a wide, shallow pan and stir over a gently heat until the syrup has melted.
Add the orange slices to the pan in a single layer and bring the liquid to the boil. Reduce the heat and simmer the slices very gently for about 15-20 minutes until the peel is tender and translucent, and the liquid has thickened to a syrupy consistency. Carefully remove the orange slices to a plate using a slotted spoon and set aside.
Loosen the edges of the hot puddings with a round bladed knife and turn out onto individual edged dishes. Spoon over the warm rhubarb syrup and add an orange slice on top. Finish with chilled custard or single cream.
If you would rather make 1 large sponge, spoon the mixture into a greased 1.1litre (2 pint) pudding basin. Take a large sheet of foil and make a pleat down the centre. Butter well and use to cover the basin, butter side down. Fold the edges under to seal well. Put the pudding in a large, deep saucepan and pour in boiling water to come halfway up the sides. Cover with a lid or foil and simmer gently for about 2 - 2.25 hrs. Keep an eye on the level of the water and add more as necessary.