Mix the flour, suet and sugar together. Beat the egg with the egg yolk then mix it into the dry ingredients. Add a little milk to give the mixture a pudding consistency when the mix just drops from the spoon. Add half the walnuts and half the maple syrup. Pour into the prepared pudding basin, cover and cook in a hot steamer or a pan half-filled with hot water for 1¼–1½ hours.
Warm the remaining walnuts in the maple syrup. Turn out the puddings on to one large or several individual plates, spoon the syrup and nuts over and serve with cream or custard.