Fill a large pot with water and bring to a raging boil. Add a palmful of kosher salt. Submerge the broccolini in the salted water and cook for 2 minutes, until the stems just start to get tender. Drain and allow the excess water to drip off.
Warm the olive oil in a large skillet over medium heat. Add garlic and chili flakes. Saute for 30 seconds until just fragrant.
Add the broccolini to the skillet and season with salt and pepper. Yes, even though you salted the cooking water. Cook for 2-3 minutes, turning the broccolini in the oil and sweeping over the bottom of the skillet to ensure the garlic doesn’t burn.
Add the red wine vinegar and cook for 1 minute. I like to serve this immediately since acid (vinegar or citrus juice) will cause the broccolini to lose vibrancy.
Top with shaved Parmesan (optional)