Add the oil, the ginger slice, and star anise to a small stainless steel or non-reactive saucepan (definitely not your carbon steel wok!) over medium-low heat, and cook until the ginger starts to caramelize, about 1 minute.
Next, add the tomato paste, stirring constantly until the tomato paste starts to caramelize—2 minutes. Take care not to burn the aromatics and tomato paste. This step is essential to giving the sauce a deeper, more complex flavor.
Next, stir in the sugar, water, white vinegar, and soy sauce. Bring everything to a simmer and cook until the sugar is completely dissolved. Add your optional fruit juice or syrup, if using.
Reduce the heat to low. Let the sauce simmer and reduce until it just starts to coat a spoon, about 10 minutes. The sauce needs this time for the flavors to meld. After the sauce has reduced, remove the star anise and ginger.
At this point, your sauce is ready to use if you’re cooking another dish (you can reheat it and thicken it just before you toss in any other ingredients), or ready for the fridge or freezer if you’re storing it for later (let the sauce cool before chilling). If using it for dipping, make your cornstarch slurry by combining the cornstarch and water. The sauce will already be somewhat thick because of the sugar, so add the slurry very gradually, simmering the sauce until it reaches your ideal consistency. You may not need all of the slurry.
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Notes
Nutrition info is for 1/8 of the recipe. It does not factor in optional fruit juice/syrup.Only thicken your sauce if you plan on using it right away (say, as a dipping sauce). If you plan on making another dish with it, wait to thicken the sauce until you’re ready to cook the dish!Sweet and sour sauce will keep in the refrigerator for a few weeks in a clean, airtight container. Be sure to handle the sauce with clean utensils to prevent spoilage. You can also store the sauce even longer in the freezer (3-4 months). Thaw it in the refrigerator overnight before using.