Heat the oil in a large frying pan. Add the onions and fry over a low heat for five minutes or until the onions are translucent.
Meanwhile, wipe and roughly chop the mushrooms, then turn up the heat to medium and add to the pan along with the cumin. Cook for about 3 minutes, stirring occasionally.
Blitz everything in a blender or food processor until almost smooth. I like to have a bit of texture, but how smooth you blend it is entirely up to you. I used a my Optimum Vac2 power blender.
You can swap the butter beans for your preferred bean, but butter beans do have the creamiest texture.
Please note: calories and other nutritional information are per serving. They're approximate and will depend on exact ingredients used.