I do not need to gain weight.
I am, however, sitting here eating the pudding, which I couldn't finish last night.
It was treacle sponge and custard, which was an experiment of mixed success in the microwave.
One egg, 3 oz. flour, 2 oz oz caster sugar and 2 oz veg. oil, whisked into a batter, then nuked on medium.
Initially, I needed a pickaxe to extract the concrete from the bowl, so I'd nuked it for too long.
I excavated it eventually, turned it upside down, poured on water and syrup, nuked it a bit more, and then served it with custard (also made in the microwave)
Partner loved it and felt full for ages.
It's still palatable reheated this morning.
It does have an egg in it (but you could probably just use an egg white) but otherwise only has vegetable oil. (Friend had suggested margarine but I had none in the house. I don't have the strength to cook with it much anyway.)
Experiment and enjoy!