Set a large pot or Dutch oven over medium-high heat. Add the ground beef and cook until no longer pink, breaking apart and stirring as the meat cooks. Stir in the minced garlic and cook for another minute or two until fragrant.
Drain the grease from the pot and season the beef with salt and pepper, to taste. Add the marinara sauce, tomato paste, balsamic vinegar, dried basil, dried oregano, dried thyme, sugar (if using), and beef broth. Stir well to combine, bring to a boil, and then reduce heat to a low simmer (about medium-low).
Lay the broken spaghetti noodles on top of the sauce, criss-crossing them and pressing them down until submerged by liquid. Do not stir at this point.
Cover and cook, stirring every 5 minutes, until the excess liquid is absorbed and the pasta is al dente, about 15 to 20 minutes total (see NOTES below).
Stir well and serve immediately, topped with plenty of Parmesan cheese.
If your sauce is still too watery by the time your pasta is done cooking, take the lid off and cook uncovered for the last few minutes. This will allow excess liquid to evaporate. I cooked this particular batch of One-Pot Spaghetti for 15 minutes covered and 2 minutes uncovered.
On the other hand, if your pasta isn't cooked through by the time all of the excess liquid in the sauce has evaporated, stir in a bit more water and continue cooking until the noodles are nice and al dente.
If you'd like to use whole wheat or gluten-free spaghetti in place of regular white pasta, just be prepared to adjust the cooking time and/or liquid, as described above.