1Bring a large pot of salted water to a boil for the spaghetti.
2Heat the olive oil in a dutch oven over medium-high heat. Add the ground beef, break it up, and brown it well, about 6 to 8 minutes. Season lightly with salt and pepper, then spoon off most of the excess fat.
3Add the diced onion and cook until soft and lightly golden, about 5 minutes. Stir in the garlic and cook 30 seconds more.
4Stir in the tomato paste and cook for 1 minute until it darkens slightly.
5Pour in the crushed tomatoes, then add the oregano, dried basil, and red pepper flakes. Season with salt and pepper. Reduce heat to low, partially cover, and simmer 20 minutes, stirring now and then.
6While the sauce simmers, cook the spaghetti in the boiling water until just al dente. Reserve a cup of the pasta water, then drain.
7Toss the spaghetti into the sauce with a splash of pasta water to loosen it. Adjust salt and pepper to taste.
8Serve topped with grated parmesan and torn basil leaves.