Add the soy sauce and brown sugar to the Thermomix bowl. Heat for 10 minutes/100°C/speed 1. The sauce will continue to thicken once it cools.
Notes
Doubling the recipe: If you're doubling the recipe, increase the heating time to 15 minutes/100°C/speed 1.Storage: Store the kecap manis in an airtight jar or container in the fridge for up to a month. Give it a stir before using if it has thickened further in the fridge, or add a small splash of warm water to loosen it.This recipe is not suitable for freezing.