Place a large pot on medium heat. Add olive oil and let it warm for one minute. Do not let it smoke. Warm oil helps release flavor from onions and garlic.

Add chopped onion to the pot. Stir well. Cook for about 5 minutes until soft and light golden. Do not burn it. Soft onion gives natural sweetness to the sauce.

Add minced garlic to the onions. Stir constantly for one minute. Garlic cooks fast and burns easily. You want a soft smell, not a bitter taste.

Add tomato paste to the pot. Stir well and cook for two minutes. This step makes the flavor stronger. It also gives the sauce a deeper red color.

Pour in the crushed tomatoes carefully. Stir everything together. Add half a cup of water. Mix well so nothing sticks to the bottom.

Add salt, black pepper, sugar, oregano, basil and chili flakes. Stir well. The sugar helps balance the tomato acidity. Do not skip this step.

Lower the heat to low. Cover the pot partly. Let the sauce simmer for 45 to 60 minutes. Stir every 10 minutes. Slow cooking builds deep flavor.

In the last five minutes, add fresh chopped basil. Stir gently. Fresh basil gives a bright and fresh taste that makes the sauce special.

Taste the sauce carefully. Add more salt if needed. If too thick, add a little water. If too thin, cook uncovered for extra minutes.

Turn off the heat. Let it rest for five minutes. Serve over freshly cooked spaghetti. Add grated cheese on top if you like.