Prepare the pappardelle noodles according to package instructions; drain very well and keep warm while preparing the sauce.
Place a large, heavy-bottom pan over medium-high heat and add 2 tablespoons olive oil. Once hot, crumble the spicy Italian sausage into small chunks, browning on each side. Remove with slotted spoon and set aside.
Add sliced onion to the pan with sausage drippings and caramelize for 5 minutes until golden, stirring to prevent burning. Add salt, Italian seasoning, and black pepper; stir to combine.
Add bell peppers and sauté with onion for 2 minutes until slightly tender and golden. Add garlic until aromatic, then add white wine and reduce until almost completely evaporated.
Add diced tomatoes with juice and return browned sausage to pan. Gently fold to combine and simmer for 3-4 minutes to blend flavors, then turn off heat.
Finish the sauce by drizzling in 2-3 tablespoons olive oil for silky richness. Stir in chopped parsley and half of the julienned basil.
Add cooked pappardelle directly to the sauce and use tongs to gently toss and combine. Check seasoning and adjust salt and pepper as needed.
Serve in bowls garnished with remaining julienned basil. Optional: top with shaved Parmesan and extra olive oil drizzle.
