Step 1: Wash and core the yellow tomatoes, then roughly chop them into medium pieces. Dice the onion or shallots and thinly slice the garlic cloves.
Step 2: Heat the olive oil in a large saucepan over medium heat. Add the diced onion and cook for 5–6 minutes until soft and translucent, stirring occasionally.
Step 3: Add the sliced garlic and cook for about 1 minute until fragrant. Avoid browning the garlic to keep the sauce delicate and sweet.
Step 4: Stir in the chopped yellow tomatoes, salt, black pepper, and optional sugar. Mix well and bring the sauce to a gentle simmer.
Step 5: Cook uncovered for 25–30 minutes, stirring occasionally, until the tomatoes fully break down and the sauce thickens naturally. For a smoother texture, blend the sauce carefully using an immersion blender or standard blender.
Step 6: Add the torn basil leaves and simmer for another 2 minutes. Taste and adjust seasoning if needed. Serve warm over pasta, vegetables, seafood, or store for later use.