Peel and slice onions to about 1/8-inch thick — thin enough to cook quickly, thick enough to avoid scorching. Yellow or Spanish onions work best. Limit to 2 large onions per 12-inch Skillet to prevent steaming. Have your fat ready and keep a splash of water, broth, or wine nearby to deglaze if needed.

Heat a Skillet over medium to medium-high heat. Add butter, oil, or a mix and let it shimmer. Add sliced onions in large handfuls, stirring for 1–2 minutes per batch until they begin to soften — this prevents overcrowding. Once all onions are in, season with a pinch of salt. Cook over medium heat, stirring every few minutes, for 8–12 minutes total until soft, translucent, and lightly golden. To speed up softening, add 1/4 to ½ cup water or broth and cover; steam wilts the onions in a few minutes. Remove the lid once liquid evaporates and continue cooking uncovered. If the pan looks dry, deglaze with a splash of water, broth, or wine, scraping up any browned bits. Don't crank the heat — high heat burns the outside before the onions cook through.

While the 12 oz spaghetti or linguine or pasta of choice cooks, heat 2 tbsp olive oil extra-virgin and 2 tablespoons of 4 tbsp unsalted butter divided in a large Skillet over medium heat. Add the 5 cloves garlic minced and ½ tsp red pepper flakes adjust (if using) and sauté for 1–2 minutes, stirring constantly, until fragrant and just golden — don't let it burn.

Add the drained 12 oz spaghetti or linguine or pasta of choice directly to the Skillet. Add the remaining 2 tablespoons of 4 tbsp unsalted butter divided and pour in ½ cup of the reserved pasta of choice. Toss everything together over medium heat for 1–2 minutes until the 4 tbsp unsalted butter divided melts and a light, silky sauce forms. Add more pasta of choice a splash at a time if needed to loosen.

Remove the Skillet from heat and stir in the grated 1 cup freshly grated parmesan cheese plus more for serving, tossing quickly so it melts into a creamy coating rather than clumping. Season with 4 tbsp unsalted butter divided and freshly ground ½ tsp black pepper freshly ground to taste.