1. Cook the Onion and Garlic: Heat the olive oil over medium heat in a large saucepan or pot. Add the chopped onion and sauté until softened and translucent, about 5 minutes. Stir in the minced garlic (if used) and cook for 1-2 minutes until fragrant. Be careful not to burn the garlic.
2. Add the Tomatoes and Cook: Add the chopped fresh tomatoes to the pot. Stir well to combine all the ingredients. Allow the mixture to come to a simmer, then reduce the heat to low, cover the pot, and let it cook for about 30 minutes, stirring occasionally.
3. Blend: Use an immersion blender or regular blender. Blend until desired thickness (chunky or smooth). Be careful when blending hot liquids. 
4.  Add Basil: In the last 5 minutes of cooking, add the fresh basil and stir to combine. 
5. Optional: Thicken the Sauce. After the tomatoes have cooked down and released their juices, stir in 1 tablespoon of tomato paste and sugar (if using). The tomato paste will add richness and depth to the sauce. Continue to cook the sauce uncovered for another 10 minutes until it thickens to your desired consistency.
6. Season and Finish: Taste the sauce and add salt and black pepper according to your preference. If it's too acidic, you can add a bit more sugar. 
7. Serving Suggestions: Use the marinara sauce immediately or let it cool before storing it in an airtight container in the refrigerator for up to a week. It also freezes well, so you can make a larger batch and keep some for future use.

This versatile marinara sauce with fresh tomatoes is great for various dishes, including pasta dishes, pizza sauce, and more. Enjoy your homemade marinara sauce with the delightful taste of fresh tomatoes!