Bring a large pot of well-salted water to a rolling boil. Add the pasta and cook until just al dente according to package directions. Reserve 1 cup of the pasta water before draining.

While the pasta cooks, heat a wide, heavy skillet over medium-high heat. Add a drizzle of oil, then the diced onion and garlic. Cook for 3-4 minutes, stirring often, until the onion is soft and beginning to turn gold.

Add the ground beef to the skillet and break it up with your spoon. Season with a pinch of salt and pepper. Cook for about 5 minutes or until the meat loses its pink color and develops a little browning. Drain excess fat if needed.

Next, add the tomato paste and cook for another minute to allow it to develop flavor. Sprinkle in the chili powder and cook for another 30 minutes, stirring from time to time.

Pour in the Rotel tomatoes (juices and all) and the beef broth. Bring to a gentle simmer, scraping up any browned bits on the pan bottom. Let the sauce bubble for 5 minutes, or until slightly thickened.

Reduce the heat to low. Off the heat, whisk in the sour cream until the sauce is smooth. Return the skillet to low heat and warm through; do not let it boil, or the sour cream may split. Taste and adjust salt and pepper.

Add the drained pasta to the skillet and toss well to coat. If it looks to dry, loosen it with a splash of the reserved pasta water.

Stir in the chopped parsley, then sprinkle the grated Parmesan. Give everything a final toss and serve immediately with some extra Parmesan on top if you like.