Bring a large pot of water to a rolling boil and add salt. Cook bowtie pasta according to package instructions until al dente, about 9-11 minutes. Reserve a cup of pasta water, then drain.

In a large skillet, heat olive oil over medium heat. Add the diced onion and sauté for about 4-5 minutes until translucent. Stir in minced garlic and cook for another 30 seconds.

Add ground beef to the skillet, breaking it apart. Cook for 6-8 minutes until browned. Drain excess fat, if necessary.

Pour in beef broth, scraping the skillet to deglaze. Stir in red pepper flakes, salt, and pepper, and simmer for 4-5 minutes.

Toss the cooked pasta into the skillet, mixing well. If dry, add reserved pasta water to help the sauce adhere.

Remove from heat, plate the pasta, and top with Parmesan cheese and parsley. Add black pepper and lemon zest if desired.