Bring a large pot of salted water to a rolling boil and cook 12 oz pasta 1–2 minutes under package instructions for al dente, then reserve 1 cup pasta water, drain, and set the pasta aside.
Season 1 lb bite-sized chicken pieces with salt, pepper, paprika, and 1 tsp Italian seasoning, then sear in a large skillet with 1–2 tbsp of the ½ cup butter over medium-high heat until golden and cooked through, about 5–7 minutes (165°F/74°C); work in batches if the pan gets crowded.
Remove the chicken to a plate, then melt the remaining butter in the same skillet and sauté 3 cloves minced garlic with ½ tsp red pepper flakes (if using) for 30–60 seconds until fragrant.
Pour in ½ cup heavy cream, scrape up any browned bits from the pan, and bring to a gentle simmer; stir in ½ cup grated Parmesan and simmer 2–3 minutes until the sauce thickens enough to coat the back of a spoon, tasting and adjusting salt and pepper.
Toss the drained pasta and seared chicken into the skillet, adding reserved pasta water a few tablespoons at a time to loosen the sauce and create a glossy, clingy coating.
Serve immediately, sprinkled with chopped fresh parsley and extra Parmesan for brightness and texture.
