Bring a heavily salted pot of water to a boil
In a large frying pan over medium high heat, add the oil and the mortadella. Cook 5 minutes until the mortadella starts to brown on the edges.
Add the onions and cook another 5 minutes. Stir in the garlic and cook 2 minutes.
Add in the collard greens and stir to combine. Season with the salt and chili flakes and continue to cook and stir for 5 minutes.
Drip the pasta into the boiling water as you continue to cook the collard greens down. When the pasta is ready, reserve 1 cup of the pasta cooking liquid and set it aside. Drain the pasta and add it right into the pan with the mortadella and collard greens.
Stir half of the pasta water into the mixture, along with the milk and cream cheese. Stir until the cream cheese has melted into the mixture. Bring to a simmer and remove from heat.
Str in the mustards first, then stir in the cheese. Do the cheese in 3 batches, stirring until the cheese is fully incorporated before doing the next batch. Once all the cheeses are added and the sauce is uniform, stir in more of the pasta cooking liquid if needed to thin it out a bit.
Serve and garnish with more chili flakes and whole grain mustard.