Begin by bringing a large pot of salted water to a boil. Add your pasta and cook according to the package instructions until al dente. Reserve about a cup of the pasta water, then drain the pasta and set it aside.

In a large skillet over medium heat, add the olive oil and butter. Once the butter has melted, add the sliced onions. Season them with salt and pepper. Stir frequently for about 10 minutes until they turn translucent. Reduce the heat to low and let them cook slowly for another 20-30 minutes, stirring occasionally until they achieve a deep golden brown color and a sweet flavor.

Once the onions are perfectly caramelized, add the cooked pasta to the skillet. Toss everything together, ensuring the pasta is well-coated with the buttery onion mixture. If it looks a bit dry, add a splash of the reserved pasta water to create a silky sauce.

Remove the skillet from the heat, and mix in the grated Parmesan cheese. Taste your dish, and adjust the seasoning if needed. You can also sprinkle some red pepper flakes if you’re in the mood for a little kick.

Plate the pasta and garnish with fresh thyme or parsley for a beautiful touch. Enjoy this comfort food warm and share it with friends or family!