Heat olive oil in a large deep skillet or Dutch oven over medium-high heat.
Add the ground beef and cook, breaking it apart with a spoon, until browned and cooked through, about 5-7 minutes.
Add the chopped onion and cook until softened, about 3 minutes.
Stir in the minced garlic and cook for 1 minute until fragrant.
Pour in the beef broth and whole milk, then add the uncooked penne pasta, dried Italian seasoning, salt, black pepper, and crushed red pepper flakes.
Bring the mixture to a boil, then reduce heat to medium-low and cover the pot.
Simmer for 12-15 minutes, stirring occasionally, until the pasta is tender and most of the liquid is absorbed.
Remove the pot from heat and stir in the grated Parmesan cheese and heavy cream until the sauce is creamy and well combined.
Sprinkle with chopped fresh parsley before serving.