Preheat the oven to 180ºC (350ºF/Gas 4). Butter 2 × 22 cm (8 1⁄2 in) sandwich tins and line the bases with baking parchment. Put the grated pumpkin in a bowl and add the orange zest and juice.
In a large mixing bowl and using an electric mixer (or in the bowl of a stand mixer), beat the butter, oil and sugar until pale, smooth and fluffy, with a light caffe latté colour. Add the eggs one at a time, beating well after each addition, until they are fully incorporated.
Add the salt, cinnamon, flour, baking powder and, finally, the grated pumpkin and orange mix, and stir to combine.
Spoon the batter into the prepared tins, dividing it equally and smoothing the tops. Bake in the oven for 25–30 minutes, until risen and golden. Insert a skewer or spaghetti strand to check it’s done (see p 252).
Remove from the oven and allow to cool for 10 minutes before turning out of the tins and leaving to cool completely on a wire rack.
Beat the ingredients for the icing together in a mixing bowl. Spread half of the icing over the base of the cake, sandwiching it with the top half, then spread the remainder of the icing on top.
Decorate with orange zest or sprinkles, as you see fit. Some slivers of candied orange would also be nice.