Finely slice the leek and wash it. Finely chop the garlic.

Add the olive oil to a cast iron pot, then add the leek. Cook over medium heat for 10 minutes until softened. Add the garlic and thyme leaves and cook for 2 minutes.

Add the white wine, butterbeans, and chicken stock to the pot and simmer for 10 minutes.

Meanwhile, heat a frying pan over high heat. Add the sausages and fry until browned (they don't need to be cooked through at this point).

Add the sausages to the bean pan along with the spinach, then simmer for 20 minutes.

Return the sausage pan with the fat to the heat. Add the breadcrumbs and toast for 5 minutes or until deeply golden. Season with salt and remove from the pan.

Once the 20 minutes is up, add the creme fraiche and parmesan to the beans, along with the juice and zest of half a lemon. Season to taste with salt and pepper.

Spoon the stew into bowls, then sprinkle with the toasted breadcrumbs and serve.