Step 1: Heat 1 tablespoon of olive oil in a large pot or Dutch oven over medium heat. Add 1 chopped yellow onion and cook until softened, about 5-7 minutes. Add 3-4 cloves of minced garlic and 1/2 teaspoon red pepper flakes (optional, for a little kick) and cook for another minute until fragrant.
Step 2: Stir in one 28-ounce can of crushed tomatoes, 4 cups of vegetable broth, 1 teaspoon dried oregano, 1/2 teaspoon dried basil, 1/2 teaspoon salt, and 1/4 teaspoon black pepper. Bring the mixture to a gentle simmer.
Step 3: Add 12 ounces of uncooked pasta (penne, rotini, or linguine work well) to the pot. Make sure the pasta is mostly submerged in the liquid. If it's not, add a splash more broth or water until it is. Bring back to a simmer, then reduce heat to medium-low, cover, and cook for 12-15 minutes, stirring every 3-4 minutes to prevent sticking, until the pasta is al dente and most of the liquid has been absorbed.
Step 4: Once the pasta is cooked, stir in 5 ounces of fresh baby spinach, 1/2 cup heavy cream, and 1/2 cup grated Parmesan cheese. Cook, stirring gently, for 2-3 minutes more, or until the spinach has wilted and the sauce has thickened slightly. Taste and adjust seasonings as needed.
Step 5: Remove from heat. Let the pasta sit for a few minutes, uncovered, to allow the sauce to thicken further. Serve immediately, garnished with extra Parmesan cheese and fresh basil, if desired.