Melt the butter and olive oil in a pan over a medium heat. Add the onions and cook for 5-6 minutes then add the leeks and garlic and cook for a further 5 minutes until softened.
Increase the heat slightly then add the wine and stir until it has reduced and alcohol has burned off, roughly 5 minutes. Then, add the beans with their bean stock plus the veg stock and reduce to a simmer for about 2 minutes.
Meanwhile, toast the walnuts in a separate pan for 1-2 minutes until golden. Roughly chop into smaller pieces.
Stir ¾ of the parsley and a squeeze of half a lemon into the bean-otto and stir to combine. Season to taste.
Divide the bean-otto between bowls. Scatter over the slices of cheese, remaining parsley and the toasted walnuts. Finish with an extra squeeze of lemon, if you like.
