Step 1: Heat olive oil in a large heavy-bottomed pot or Dutch oven over medium heat. Add diced onion, carrots, and celery. Sauté for 8-10 minutes, or until vegetables are softened and translucent.
Step 2: Add minced garlic and cook for another 1-2 minutes until fragrant. Be careful not to burn the garlic.
Step 3: Stir in the tomato paste and cook for 3-5 minutes, stirring occasionally, until it darkens slightly. This deepens the tomato flavor.
Step 4: If using, pour in the red wine, scraping up any browned bits from the bottom of the pot. Let it simmer until the liquid has mostly evaporated, about 3-5 minutes.
Step 5: Add the crushed San Marzano tomatoes, diced tomatoes, vegetable broth, dried oregano, dried basil, and red pepper flakes (if using). Stir well to combine.
Step 6: Bring the sauce to a gentle simmer, then reduce the heat to low. Cover the pot and let the sauce simmer for at least 60-90 minutes, stirring occasionally, to allow the flavors to meld and deepen. For a richer flavor, you can simmer it longer, up to 2-3 hours.
Step 7: After simmering, stir in the nutritional yeast and fresh chopped basil. Taste the sauce and season with salt, freshly ground black pepper, and a pinch of sugar if needed to balance any acidity.
Step 8: Serve your ultimate hearty vegan spaghetti sauce hot over your favorite pasta, or use it in other dishes like lasagna or subs. Garnish with extra fresh basil if desired. Leftovers can be stored in an airtight container in the refrigerator for up to 5 days, or frozen for up to 3 months.