Cook the pasta according to package instructions until just al dente (do not overcook or it will get mushy).
While the pasta is cooking, heat a large sauté pan over medium high heat and add the olive oil. When the oil is hot, add the pancetta and rosemary, and sauté for a few minutes until the pancetta starts to brown.
Add the garlic, jalapeno, black pepper to taste, and cayenne and sauté until garlic and pancetta turn golden brown, about 3 minutes.
Add the Brussels sprouts and sauté until they just start to soften, about 2 minutes. Spread sprouts mixture in pan and press down to flatten. Let it sear for a minute, then stir it up and repeat (this helps brown the sprouts).
Add the pasta and butter, toss to combine and sauté for another minute.
Serve in bowls topped with a drizzle of olive oil and lemon juice, and sprinkled with parmesan cheese.
