Bring a large pot of salted water to a vigorous boil and cook the pasta until just shy of al dente (about 1–2 minutes less than package instructions). Reserve 1 cup of pasta water, then drain the pasta.

While the pasta cooks, heat olive oil or butter in a large skillet over medium-high heat. Add the chopped onion and a pinch of salt. Sauté until translucent and soft, about 4 minutes.

Add the garlic and red pepper flakes (if using). Stir for 30 seconds until fragrant.

Crumble in the ground beef. Let it brown without crowding the pan; sear for 4–6 minutes until edges caramelize and juices evaporate. Use a wooden spoon to break it into bite-sized pieces. Season with salt, pepper, and oregano.

Pour in the beef broth, scraping up any browned bits from the bottom of the pan. Let the broth reduce for 2–3 minutes.

Reduce heat to low and stir in the cream or half-and-half. The sauce will gently bubble and thicken.

Stir in the Parmesan, then add spinach, peas, or roasted peppers. If using Greek yogurt, whisk it in off heat to prevent curdling.

Add the drained pasta to the skillet and toss to coat, adding reserved pasta water a splash at a time to reach your desired sauce consistency.

Taste and adjust seasoning. Finish with a shower of fresh parsley or basil and an extra grind of black pepper. Serve immediately.