In a mixing bowl or liquid measuring cup, soak cashews and carrots in very hot water for 30 minutes (uncovered). Then drain and add to a high-speed blender with 1 cup water, tapioca starch, nutritional yeast, apple cider vinegar, sea salt, garlic powder, and dry mustard (turmeric is optional for deeper color). Blend on high until the mixture is smooth.
Taste and adjust flavor as needed, adding more apple cider vinegar for acidity, nutritional yeast for cheesiness, garlic powder for depth of flavor, or salt to taste.
Transfer to a medium saucepan and heat over medium heat. Cook, while whisking, for 1-2 minutes or until thickened to a spreadable consistency (see photo). It should resemble the texture of soft cooked polenta.
Store sauce covered in the refrigerator for up to 1 week, or in the freezer for up to 1 month (let thaw in the refrigerator before use). In the fridge, it will thicken into a paste/spread as it chills.
*Nutrition information is a rough estimate calculated without optional ingredients.
*Recipe as written makes ~1 ¼ cup.