Heat your oven to 200°C/Fan 180°C/Gas 6. Tip the quinoa into a sieve and rinse well under cold water for 1 min. Shake any excess water off and leave to one side to dry a little.
Tip the butter beans and their liquid into a pan. Pop on a lid and set over a medium heat. Bring to a simmer, then gently cook for 5 mins to warm the beans through.
While the butter beans simmer, peel and finely chop the onion. Thickly slice the mushrooms. Peel and grate or crush the garlic.
Set a medium pan on a medium heat. Add 1/4 tbsp olive oil, the onion and mushrooms with a pinch of salt and pepper. Fry for 5 mins, stirring every so often, till the onion begins to soften and brown.
While the veg fry, take the butter beans off the heat and use a hand-held blender to whizz the beans and their liquid together to make a thick purée. No hand-held blender? You can tip the butter beans and their liquid into a blender or food processor and blitz. Or drain the butter beans into a bowl (keeping the liquid in the pan) and mash them with a potato masher or fork, then stir in the warm liquid till smoothly combined.
Stir the garlic and quinoa into the onion. Cook and stir for 2 mins, till the pan smells sweet and aromatic. Crumble in the stock cube. Pour in 300ml boiling water. Pop a lid on the pan and bring to the boil, then turn the heat down and simmer for 12 mins till the quinoa is tender.
While the quinoa cooks, slice the soft kale leaves off the cores and roughly chop the leaves. Pop them in a bowl with the tahini, 1/4 tbsp olive oil and a pinch of salt and pepper. Turn to coat the kale in the tahini and oil. Spread out on a baking tray and slide into the oven for 5-8 mins till crisp and charred at the edges.
Stir the butter bean purée into the quinoa and simmer for 2-3 mins to warm everything through.
Taste the quinoa risotto and add a pinch more salt or pepper if you think it needs it. Spoon the risotto into warm bowls and top with the kale to serve.