Trim the tough ends from the broccoli rabe, then cut the stems and leaves into roughly 1-inch pieces. Wash the greens thoroughly to remove any grit.

Bring a large pot of well-salted water to a boil. Blanch the broccoli rabe for 2-3 minutes, until the stems are just tender and the leaves are wilted, then transfer it to cold water, drain well, and squeeze or pat dry.

Return the water to a boil and cook the pasta until al dente according to the package directions. Before draining, reserve at least 1 cup of the cooking water.

Heat 1 tablespoon of olive oil in a large skillet over medium heat. Add the diced pancetta and cook for 5-7 minutes, stirring occasionally, until browned and crisp.

Add the remaining olive oil, garlic, and red-pepper flakes to the skillet. Cook for 30-60 seconds, just until fragrant, taking care not to let the garlic burn.

Add the blanched broccoli rabe and sauté for 2-4 minutes. Season lightly with kosher salt and freshly ground black pepper.

Add the drained pasta and about 1/2 cup of reserved pasta water to the skillet. Toss over medium heat until the pancetta, oil, and water form a light coating around the pasta, adding more water as needed.

Remove the skillet from the heat and toss in the Parmesan cheese. Add the lemon juice if using, then serve with more Parmesan, black pepper, and a drizzle of olive oil.