Prep the Pasta Water & Broccoli Rabe: Bring a large pot of generously salted water to a boil.
Meanwhile, prepare the broccoli rabe. Trim and discard the tough, thick bottom stems (anything thicker than a pencil). Wash the remaining greens thoroughly in a large bowl of cold water, then drain well. Coarsely chop the broccoli rabe.
Sauté the Aromatics: In a large skillet or Dutch oven, melt the butter with the olive oil over medium heat.
Add the diced onions and sauté, stirring occasionally, for about 10 minutes until soft and translucent.
Stir in the minced garlic and cook for another minute until fragrant.
Cook the Greens: Add the chopped broccoli rabe to the skillet with the onions.
Cook, tossing frequently, for about 10 minutes, or until the stems are tender and the greens are wilted.
Cook the Pasta: While the broccoli rabe is cooking, add the farfalle to the boiling water.
Cook according to package directions until al dente (firm to the bite).
Combine and Serve: Season the broccoli rabe sauce with salt and pepper. Just before draining the pasta, reserve about a cup of the starchy pasta water.
Drain the farfalle well and add it directly to the skillet with the sauce, or return it to the pot.
Add the grated Parmesan cheese and toss everything together, adding a splash of the reserved pasta water if needed to create a silkier sauce.
Serve immediately with extra Parmesan on top.
Add a Kick: For a touch of heat, add 1/4 to 1/2 teaspoon (10 ml / 0.3 fl oz) of red pepper flakes to the skillet along with the garlic.
Don't Skip the Pasta Water: That starchy, salty water is liquid gold! It helps the sauce cling to the pasta and emulsifies the oil and cheese, creating a creamy consistency without any cream.