Cook the bow tie pasta according to package instructions until al dente. Drain and set aside.
In a large skillet, heat olive oil over medium-high heat.
Add the diced onion and cook for 3-4 minutes until softened.
Add the minced garlic and cook for 30 seconds until fragrant.
Add the ground beef to the skillet. Cook, breaking it apart with a spatula, until browned and cooked through, about 6-8 minutes. Drain excess fat if necessary.
Sprinkle the ranch seasoning mix over the cooked beef and stir to combine.
Pour in the beef broth and whole milk, stirring to incorporate the seasoning into the liquid.
Bring the mixture to a simmer and cook for 5 minutes, allowing the sauce to slightly thicken.
Reduce the heat to low, then stir in the sour cream until the sauce is creamy and smooth.
Add the cooked bow tie pasta to the skillet and stir to coat the pasta evenly with the sauce.
Sprinkle the shredded cheddar and mozzarella cheeses over the pasta mixture. Cover the skillet with a lid and cook for 3-4 minutes until the cheese melts.
Season with salt and black pepper to taste.
Garnish with chopped fresh parsley before serving.