Serves 3 to 4
- Melt butter with 2 tablespoons oil in a large skillet over medium-low heat.
- Add yellow onion, red onion, leeks, and thyme. Cover and cook, stirring occasionally, until onions have cooked down, about 10 minutes.
- Uncover and continue to cook until deeply caramelized and soft, about 30 additional minutes. Season with salt and pepper.
- Add cognac to onions and cook for 1 minute, scraping brown bits from bottom of pan. Remove thyme sprigs and transfer onion mixture to large bowl and wipe out skillet.
- Meanwhile, bring a large pot of salted water to boil for pasta.
- Heat remaining tablespoon oil in now empty skillet over medium-low heat. Add bread crumbs and garlic and cook, stirring, until browned. Season with salt and pepper and set pangrattato aside.
- Cook pasta according to package instructions, saving ½ cup of the cooking water before draining.
- Add hot pasta to bowl with onion mixture; add cheese and heavy cream. Gently toss while adding enough cooking water to create a silky sauce. Season with salt and pepper.
- Serve fettuccine topped with pangrattato, thyme leaves, and chives.
*Notes: Try serving this alongside a perfectly-cooked steak.