1. Heat the olive oil in a large saucepan over medium heat. Add the chopped onion and sauté until translucent, about 5 minutes. Stir in the minced garlic and cook for an additional minute, until fragrant.
2. Add the crushed tomatoes, tomato paste, sugar, salt, black pepper, oregano, and red pepper flakes to the saucepan. Stir to combine.
3. Bring the sauce to a gentle simmer, then reduce the heat to low. Allow it to simmer uncovered for about 45 minutes, stirring occasionally. This slow simmering process is crucial for developing deep, rich flavors.
4. As the sauce simmers, stir in the fresh basil leaves during the last 10 minutes of cooking.
5. Taste and adjust the seasoning if necessary. If the sauce is too acidic, add a bit more sugar. If it needs more depth, a splash of red wine can enhance the flavor profile.
6. Remove from heat and let the sauce cool slightly before serving it over your favorite pasta. Top with freshly grated Parmesan cheese if desired.

One tip from my mother, Elena: always taste as you go. Cooking is an intuitive art, and the best dishes come from making little adjustments along the way.