Bring a large pot of salted water to a boil. Add broccoli rabe to the boiling water and let cook until slightly softened, about 2-3 minutes. Drain well and set aside.

Meanwhile, heat oil, garlic, and red pepper flakes in a large skillet over medium heat. Sauté until the garlic starts to get some caramel-brown bits, about 5-10 minutes. Add the broccoli rabe, season with ½ teaspoon kosher salt, and sauté, stirring occasionally, for 5 minutes. Reduce heat to low and continue to sauté, stirring occasionally, for an additional 20-30 minutes.