Bring a large pot of water to a boil. Season liberally with salt and cook the pasta per the package directions until al dente. If using broccoli, add to the pasta 2 minutes before it finishes cooking. Drain, reserving 1 cup of the cooking water.
While the pasta cooks, make the sauce: Heat a medium skillet over medium heat. Add the mascarpone, butter, lemon zest and a sprinkle of salt and black pepper. Stir together and once it simmers, reduce the heat to low to keep the sauce warm without reducing it. Add the spinach, if using, and cook until wilted, 1 to 2 minutes.
Add the pasta (and broccoli, if using) to the sauce but do not stir. Squeeze the lemon juice all over, then stir together and add in the 1/2 cup Parmesan. Cook until thick and creamy and all of the flavors absorb, 1 to 2 minutes. If the pasta looks too dry, stir in a little of the reserved cooking water.
Divide the pasta among bowls and drizzle with pesto, if using. Top with the prosciutto, burrata or shrimp, if using. Garnish with basil leaves and Parmesan, sprinkle with crushed red pepper, if desired, and serve immediately.