I’ve stopped cooking them (everyone prefers a steamed syrup pudding) but this is what I have learnt. And it would always turn out more crumbly than I would prefer. I do a good fruit cake, though.
My flour mix is 500g tapioca flour, 500g glutinous rice flour, 200g millet flour, 200g bean/chick pea flour. I use xanthan gum but only a pinch. Almond or hazelnut flour have fat in them so a spoon of that into your flour mix might be of advantage. Soy is a natural emulsifier which is why you see it so often in product. A spoon of that might be useful. Lupin flour bakes beautifully but we don’t get on with it. But a spoon of that into your flour mix might be good, too.
I would soak the fruit for 12-24 hours. Use fruit that soaks well. Sultanas, raisins, fresh dates rather than dried, diced, dried fig diced. Prunes. Currants are a pain so I gave them a miss.
I couldn’t get suet to work. Everything would swim in the melted fat, not soak it up and then, once cold, I would have congealed fat everywhere. I reduced the amount to about 30% of the recipe and it still wouldn’t work. So, I used melted butter.
So, soak the fruit. Add your flour, xanthan, sugar (I used brown as its stickier), spices and mix. Whisk eggs and milk and start folding through. Duck eggs are stickier so are good for baking. Alternate with melted butter. Stop when you think your batter is good. Allow to sit for two hours. GF flour can take a long time to hydrate. Add more liquid if you need.
My pudding bowl holds 1 litre. My recipes all seem to make 2 litres so I cooked one on day one with the excess batter in the fridge ready for tomorrow. Never a problem. Into the slow cooker for about 6 hours. I found it wouldn’t need more.
Good luck with it. I would be interested to know how you get on. Merry Christmas.