Step 1
Place a soup pot on the stove over medium/high heat. Add the olive oil and the pork sausage meat, breaking it up as it cooks to a golden-brown colour. Remove the pork from the pot and set aside. Turn off the heat, but don’t wash the pot.
Step 2
While the pork is cooking, coarsely chop the onion, carrot and celery and add to a food processor with the garlic. Pulse until everything is finely minced. (Alternatively, chop everything finely by hand.)
Step 3
Return the soup pot to a medium heat, adding all the minced vegetables and a good pinch of salt and black pepper. Cook for about 10-15 minutes until the vegetables are tender and beginning to caramelise in the bottom of the pan. Add the tomato paste, oregano and chilli flakes, if using, and saute for another 2 minutes.
Step 4
Coarsely chop the tomatoes (if you’re using crushed, canned tomatoes, there’s no need to chop them) and add them to the pot with another pinch of salt. Stir, allowing the tomatoes to soften and release their juice (about 10 minutes).
Step 5
Add the lentils, chicken stock and parmesan rind and bring to a simmer over a low-medium heat for 45 minutes until the lentils are tender. Adjust seasoning.
Step 6
To make the pistou, combine all the ingredients in a blender with a pinch of salt and black pepper and blend until smooth. Set aside.
Step 7
At this stage, I like to remove and discard the parmesan rind and either scoop out one-quarter of the soup to blend until smooth or place a stick blender directly in the pot and pulse about 8 or so times. The goal is to blend just some of the soup so it feels a little more unified and creamy while retaining some texture.
Step 8
Return the sausage meat to the pot and bring back to a simmer. Add the vinegar. Taste and adjust the seasoning. Divide into bowls, drizzling over some of the bright-green basil pistou, and garnish with freshly grated parmigiano reggiano.
