Step 1

In a large lidded casserole dish, heat the oil over a medium-high heat. When it shimmers, add the sausage meat in an even layer making sure it gets as much contact with the bottom of the pan as possible. Leave it alone until you begin to see it browning around the edges. Using a spatula or wooden spoon, start breaking up and flipping the meat to brown, so each side is equally golden and crispy. This will take 10-12 minutes in total. Season with salt.

Step 2

Turn the heat down to medium. Add the onion, fennel and celery, and cook, stirring frequently, for another 5-7 minutes, until the onion and the fennel start to slightly caramelise.

Step 3

Add in the chopped garlic with the ground fennel seeds, rosemary, chilli flakes and tomato purée, and cook for 1 minute more.

Step 4

Add the tinned tomatoes, crushed in your hands, or passata, with the lentils and stock, and bring to a boil. Reduce to a gentle simmer and cover with the lid askew, then cook for 40-45 minutes, until the lentils are tender. Taste and season with salt accordingly.

Step 5

While the lentils cook, make the topping. Toast the walnuts in a large frying pan over a medium-low heat for 4-5 minutes, stirring frequently to prevent burning. Transfer to a medium bowl, add the parsley and 2tbsp lemon zest, and toss to coat. Season to taste.

Step 6

To serve, ladle the stew into deep bowls. Top with some of the crunchy walnut and lemon topping, a good squeeze of lemon juice, a drizzle of olive oil and some freshly ground black pepper. Serve with grated Pecorino or Parmesan at the table.