Bring a large pot of water to boil for the pasta - but first we'll blanch the spinach and garlic in it.
Drop in the spinach leaves and garlic. Blanch for 2 minutes, then carefully scoop everything out and transfer to a blender, along with 3 tablespoons of olive oil, 30g of Parmigiano and a good pinch of salt – blitz to a smooth and luscious sauce and set aside.
Pound the chilli flakes and fennel seeds in a mortar and pestle and set aside.
Remove the sausage meat from its casing by either squeezing the meat out from one end, or using a knife to make a vertical slit down the middle of the casing to access the meat inside.
Heat a tablespoon of olive oil in a good sized frying pan, and add the sausage meat. Try not to touch it for a few minutes, then you can use a potato masher or back of a spoon to help break the meat up into smaller pieces, then add the ground chilli and fennel.
Cook over a medium heat for around 10-12 minutes, or until the sausage meat is dark in colour and crispy, then set aside.
Returning to the pot of water, season with salt and bring back to a boil, then drop in the garganelli. They will take approximately 2-3 minutes to cook from fresh.
Reserve a 1/4 cup of the pasta cooking water before draining, then toss the garganelli with the spinach sauce, adding pasta water as needed to ensure the sauce coats the pasta perfectly. Season to taste with extra salt and pepper.
Serve topped with crispy sausage and grated Parmigiano.