Get all your ingredients in a sauce pan. Give it a little get-to-know-each-other stir.
Place the pan on the stove or induction and very slowly start simmering. Give it a gentle stir every minute until the total weight of the sauce has reduced to 220g. A reduction of 31% from its initial 320g combined starting weight.
While the sauce is reducing keep an eye on it so it does not boil over or cook too fast. Low and slow does the magic here.
Once the correct weight is achieved, let the sauce cool down and then store in airtight containers in the fridge. You now have yourself the perfect substitute for real Indonesian kecap manis.
Notes
You can use regular sugar if you don't have brown sugar but molasses is essential.
Molasses and barley malt are not the same thing.
Do not stir the sauce vigorously while reducing.
Add a teaspoon of liquid glucose if you are worried about the sugar crystalising.
Store in the fridge sealed airtight. Will keep it for an indefinite amount of time because of the salt and sugar content.
No need to freeze.
Use as a glaze when grilling meat, vegetables or fish.
Add to stews, stir fry, curry and many more dishes as a flavour enhancer.