Bring a large pot of generously salted water to a rolling boil. Add bowtie pasta and cook according to package directions until al dente, about 10-12 minutes. Drain thoroughly without rinsing.
While pasta cooks, heat olive oil in a large skillet over medium heat. Add finely diced onion and cook for 2-3 minutes until translucent with lightly golden edges.
Stir in minced garlic and cook for 30 seconds until fragrant, stirring constantly to prevent burning.
Add ground beef to the skillet, breaking it into small crumbles with a spatula. Cook for 5-6 minutes until completely browned with no pink remaining.
Carefully drain excess fat from the pan if needed, leaving just enough to maintain moisture.
Pour in beef broth along with red pepper flakes if using, salt, and black pepper. Scrape up any browned bits from the pan bottom. Let simmer for 3-4 minutes until slightly reduced.
Add drained pasta to the skillet and toss thoroughly to coat every piece with the garlic butter beef sauce.
Drizzle with additional olive oil if the mixture seems dry, tossing again for glossy appearance.
Transfer to serving plates or a large platter. Top generously with freshly grated Parmesan and chopped parsley. Finish with extra cracked black pepper if desired. Serve immediately.
