Add 2 tablespoons of duck fat (or oil) to a hot skillet over medium heat, followed by the duck legs to crisp up the meat. Remove from the pan and set aside until cool enough to handle, then strip the meat from the bones and shred. Set aside.
Meanwhile, add 5 tablespoons of unsalted butter to a separate, light colored saucepan over medium heat. Stir constantly until the butter is golden brown and gives off a nutty aroma. Remove it from the saucepan, and transfer it to a separate container, and set aside to cool. Here's our step-by-step guide on how to brown butter. In the same pan you cooked the duck in, without draining the duck fat, add the mushrooms in an even layer and let it cook undisturbed for about 5 minutes to help them get nice and golden brown, then turn them off and continue cooking for 3-5 minutes. Season with a bit of salt near the end of cooking, then remove from the pan. Don't drain the fat.
Meanwhile, prepare the pasta. Start by bringing a large pot of salted water to a boil for the pasta, and cook for 1-2 minutes under the package directions to allow the pasta to continue cooking in the sauce. Set the pasta aside and be sure to reserve some pasta water for bringing the sauce together later.
To the same pan, add the onions with a pinch of salt. Cook until softened, then add in the garlic and fresh herbs. Cook until the garlic is fragrant, then immediately deglaze the pan with ½ cup of chicken broth. Reduce the heat to low and stream in ½ cup of heavy cream.
Slowly mix in the parmesan in small handfuls, stirring to melt, then add the next. Add back the mushrooms and cooked duck to the skillet. Add the cooked pasta, the juice of ½ a lemon, the zest of 1 lemon, the reserved brown butter, and reserved pasta water as needed. Toss gently to help the sauce cling to the noodles.
Garnish with fresh rosemary, thyme, parmesan, and black pepper. Enjoy!