Shred your parmesan cheese and set aside. Yes, buying a wedge and shredding it yourself is worth it. YOU are worth it.
Thinly slice your onions and place in a large pan with raised edges (more raised than a generic fry pan). Add 1 Tbsp of olive oil and stir the onions on low heat. You’re making jammy onions. This is the most tedious step-- waiting for the onions to reduce into a caramelized base for sauce.
After 15 minutes, add the brown sugar and continue to stir. From here, the onions will reduce significantly. The edges should not be frying or browning, rather the entirety of the onion flesh should slowly brown and shrink. Keep going for at least ten more minutes!
When the onions are jammy, add the black pepper and fry until fragrant. In a separate pot, begin to boil water for your pasta. Add at least 1 tsp of salt to the water, if not more. Taste it! This will determine how salty your final product.
Cook your pasta fully (PAST al-dente). Reserve at least 1 cup of pasta water.
Bring the jammy onion pan back to low heat. Add the butter, shredded parm, pasta, and ⅔ cup of pasta water into the onion pan. With tongs, toss and stir everything vigorously until the cheese is fully integrated and the sauce is emulsified. If the sauce is still gloopy/not glossy, add a bit more pasta water and take the pan off the heat.
To serve, top with some extra parm, crispy fried onions, and lemon zest! You’re welcome.