Bring a large pot of water to a rolling boil and season generously with salt. Add the short pasta and cook according to package directions, aiming for al dente (usually 8-10 minutes).

About 3 minutes before the pasta is done, add the broccoli florets to the pot with the pasta to blanch them until tender-crisp.

Before draining, scoop out 1 cup of the starchy pasta water. Drain the pasta and broccoli, but do not rinse.

While the pasta cooks, heat the olive oil in a large skillet or Dutch oven over medium-low heat. Add the garlic and red pepper flakes (if using). Cook for 2-3 minutes until fragrant and garlic is translucent, but not browned.

Add the drained pasta and broccoli to the skillet. Pour in about 1/2 cup of the reserved pasta water. Use the back of a wooden spoon or spatula to gently mash some of the broccoli florets against the side of the pan, releasing their starches to create a cohesive sauce.

Remove from heat. Stir in the Parmesan cheese, lemon zest, and lemon juice. Toss to coat the pasta in the sauce. If needed, add more pasta water 1 tablespoon at a time for desired consistency.

Taste and adjust salt and pepper. Serve immediately, garnished with extra Parmesan if desired.