Cook your pasta in a pot of well salted water. This sauce comes together quickly, so time your pasta accordingly depending on whether you are using fresh or dried.
Melt the butter in a large pan over medium heat.
When it starts to sizzle, add the nduja and whisk into the butter until combined. Lower the heat if it’s spluttering too much.
Add the cream and whisk to combine. Keep the heat at a very gentle simmer, it should never be boiling.
Add the lemon juice and sugar (if using) and mix quickly to combine.
Add the parmesan in 2-3 separate lots, whisking between each addition until melted and smooth.
Taste for seasoning. It may not need salt, but add black pepper to taste.
Add ¼ cup of pasta water, mix well and let it thicken for 1-2 minutes.
Add the cooked pasta straight into the sauce and toss well to coat, let it gently bubble away for 1-2 minutes to thicken and coat the pasta.
Stir through the parsley and serve immediately.
The pasta should look nice and saucy in the pan, it will thicken and dry up quickly once off the heat.
Serve with extra parmesan and a good crack of black pepper.