Measure out cold soy milk or another plant-based milk, extract, the flavor of choice, lecithin, sweetener, some tapioca starch, and oil (if desired). Combine all in a saucepan.
Mix the starch into the milk before turning on the heat.
Turn the heat to medium and stir frequently until it comes to a slow boil.
Let it boil for a few seconds while stirring constantly. Then turn off the heat.
Store in an airtight jar or bottle for up to 5 days.
Notes
You can also use coffee syrups to flavor the creamer. For this method, use 2 tbsp of syrup and omit the extract and sugar.
If using the added-fat method, stir the oil and lecithin well to emulsify them.
Put into an airtight jar while still warm. If you let it sit and cool, a film will form at the top of your creamer.