Bring a large pot of generously salted water to a boil. Cook penne pasta according to package directions minus 1 minute for al dente texture, usually 8 to 10 minutes total. Before draining, reserve about 1 cup of pasta water. Drain pasta and set aside.

While pasta water comes to a boil, heat 2 teaspoons olive oil in a large skillet over medium heat. Add the diced onion and minced garlic, sautéing until fragrant and onion is translucent, about 5 minutes. Stir occasionally to prevent burning.

Add 1 pound ground beef to the skillet, breaking it apart with a spoon or spatula. Cook until browned and fully cooked through, about 7 to 8 minutes. Drain excess fat if using higher-fat beef, leaving about 1 tablespoon. Season generously with salt, pepper, and 2 teaspoons Italian seasoning.

Lower the heat to medium-low and pour in 1 cup heavy cream while stirring gently. Let sauce simmer for 2 to 3 minutes to thicken slightly. Add reserved pasta water 2 to 3 tablespoons at a time, up to 1/2 cup total, until you reach desired sauce consistency.

Stir in 1 cup grated Parmesan cheese until melted and incorporated. The sauce should coat the back of a spoon. Taste and adjust seasoning if needed.

Add the drained pasta into the skillet with the sauce mixture. Toss everything together gently for about 1 minute until each piece of pasta is coated in the creamy sauce. If sauce is too thick, add a splash more pasta water.

Transfer creamy beef pasta onto plates or into bowls. Garnish with additional Parmesan cheese or fresh parsley if desired. Serve hot and enjoy.