Lightly butter a 1.5-litre pudding basin.
Put one-third of the stem ginger and all
the ginger syrup in the bottom. Set aside.
In a bowl, beat the eggs and sugar with
an electric whisk until pale and fluffy.
Fold in the butternut squash, lemon zest
and the remaining stem ginger. Fold the
dry ingredients into the egg mixture with
a large metal spoon until well combined.
Fill the basin with the sponge mixture.
Cover with a layer of buttered baking
parchment and foil, making a pleat in
the centre to allow the pudding to rise.
Tie on securely with string, then put in
a steamer or large pan with an upturned
bowl in the bottom. Add boiling water to come halfway up the sides of the basin,
cover with a lid and simmer for 1½ hrs.
Check the water level every now and
then, and top up if you need to.
To test when the sponge is ready, insert
a skewer into the centre. It should come
out clean with no trace of raw mixture.
Unwrap and serve hot.