Preheat the oven to 180 degrees Celsius (350 degrees Fahrenheit)
Heat up the oil and add the onion and garlic once hot
Fry for around 10 minutes until softened
Meanwhile, place the white beans in a food processor or blender (or hand-held stick blender) and whizz until completely smooth
Now add the cooked onion and garlic, along with the mushrooms, walnuts and salt + pepper
Blend very briefly so that the mushrooms and walnuts are cut up into smaller pieces, but still retain a little texture
Lay out some greased baking paper on a large baking tray
Wet your fingers (to stop the mixture sticking) and use them to mould the meatball mixture into small balls and lay them out on the baking sheet - you should be able to make around 18 meatballs
Bake in the oven for around 30 minutes, until golden brown
For the gravy:
Measure out the milk in a measuring jug or container and add all the other ingredients
Mix very well, ensuring that the cornflour has completely dissolved
Heat the mixture in a pan on a low heat, stirring regularly to make sure the cornflour doesn’t clump
Slowly bring to the boil and simmer on a low heat for around 5 minutes until the gravy is thickened - add some extra milk or water to thin out if necessary
Add the cooked meatballs just before serving, and sprinkle over chopped parsley, if desired
Serve alongside mashed potatoes and cranberry sauce, if desired