Heat the olive oil in a medium-sized saucepan over medium-high heat.
Once the oil is hot and shimmering, add the finely diced onions and minced garlic to the pan. Sauté for 3-4 minutes, stirring frequently, until the onions start to become translucent and the garlic becomes fragrant.
Add the crushed tomatoes, dried oregano, dried parsley, salt, and pepper to the saucepan. Stir everything together to combine all the ingredients evenly. The mixture will look quite liquidy at this point, which is exactly what you want.
Once the sauce starts to bubble actively, reduce the heat to maintain a gentle simmer. Allow the sauce to simmer for 20 minutes, stirring occasionally to prevent sticking. During this time, the sauce will reduce and thicken to the desired consistency.
Taste the marinara sauce and adjust seasoning as needed, adding more salt, pepper, or herbs to suit your preference.
Remove from heat and garnish with freshly chopped parsley or basil if desired. Serve immediately over pasta, with breadsticks, or use as needed for your recipe.
Notes
Tomato Quality Matters - Taste your canned tomatoes before adding salt, as some brands are higher in sodium than others. Quality tomatoes make a noticeable difference in the final flavor of your marinara sauce.
Texture Control - For a smoother sauce, use an immersion blender to puree the mixture after cooking. For chunkier texture, break up whole peeled tomatoes with your hands before adding to the pan.
Flavor Development - Don't rush the simmering process. The 20-minute cooking time allows the sauce to reduce properly and the flavors to meld together for the best taste.
Fresh Herb Timing - If using fresh herbs instead of dried, add them during the last 2-3 minutes of cooking to preserve their bright flavor and prevent them from becoming bitter.