Make the Meatballs
Preheat oven to 350° F
In a food processor, add the diced pepperoni, parsley leaves, garlic, and onion. Pulse until the mix is chunky.
In a large mixing bowl, add the ground pepperoni mix, along with the ground beef, ground pork, breadcrumbs, Parmigiano cheese, cayenne, crushed fennel seeds, smoked paprika, sea salt, and black pepper.
Using your hands, gently combine just the mix is just even
Shape the mixture into 16 meatballs, placing them on a parchment-lined baking sheet.
Transfer them to the oven and back for 30 minutes, or until they're cooked through
Make the Sauce
In a large cast-iron skillet, over medium-high heat, add the olive oil, chopped onion, garlic, celery, thyme, and tomato paste, along with a generous pinch of sea salt.
Cook until the onion is soft and the tomato paste has started to brown.
Add the red wine and cook until it has nearly evaporated (~ 8-10 minutes).
Then add the pureed tomatoes, Parmigiano cheese rind, bay leaves, chili flakes, honey, ground black pepper.
Once the sauce has come to a simmer, reduce the heat to low.
Cover the pot, allowing for a small opening for steam to escape, and simmer for an hour and a half. Note: You'll want to give the sauce a gentle stir every once in a while to prevent burning on the bottom.
Add the cooked meatballs to the skillet, and allow the sauce to simmer another half hour or so. (The goal is to have the sauce's liquid reduced by about a third)
Before serving, gently mix the Dijon mustard into the sauce
Cook a pound of dried spaghetti noodles, according to package directions, to a couple of minutes before it's al dente. Drain the noodles and transfer to a large pot.
Add enough sauce to generously cover the noodles. Cook for another 2 min until the sauce has coated all of the pasta.
Transfer to a serving plate with the meatballs on top.
Sprinkle the dish with chopped curly Italian parsley, and a generous amount of grated Parmigiano cheese.