Prepare Cornstarch Slurry: In a small bowl, mix the cornstarch with a couple of tablespoons of water until smooth. This will be added later to thicken the sauce.

Blend the Preserves: In a blender or food processor, combine the apricot and peach preserves. Blend until smooth. This creates a unified fruity base without any large fruit pieces.

Combine Ingredients: In a saucepan over medium heat, combine the blended fruit preserves, light corn syrup, white vinegar, soy sauce, and yellow mustard. Stir well to ensure all the ingredients are mixed.

Add Cornstarch Slurry: Once the mixture is well combined and starting to heat, slowly stir in the cornstarch slurry. This will help thicken the sauce.

Simmer: Reduce the heat to low and let the sauce simmer for 5-7 minutes, stirring occasionally. As it simmers, the sauce should thicken to a consistency similar to the original McDonald's sauce.

Season: Add salt to taste, adjusting as needed. Remember, the soy sauce will also add some saltiness, so go easy on the additional salt.

Optional Coloring: If you want the sauce to have the signature reddish-orange hue of the McDonald's version, you can stir in a few drops of red food coloring at this point. This step is optional and only for appearance.

Cool and Store: Once the sauce has reached the desired consistency, remove it from the heat. Allow it to cool to room temperature. It will thicken slightly more upon cooling. Transfer the sauce to a clean, airtight container, and refrigerate.