To make oyster sauce, you will need a container of shucked oysters, the liquid of which needs to be retained. For those of you who are unaware of shucked oysters, they are oyster meat, that has been removed from the shells.
For this recipe, it would be advisable to use a container of previously shucked oysters than fresh ones. You need not cut the oysters into accurate pieces as they will need to be filtered, only to retain the sauce.
Preferably chop the oysters much in advance. Cut them into small pieces as that will help the flavor ooze out faster.
In a saucepan, add 2 tbsp of water along with the oysters and the juice from the shucked oysters. Place it on the stove and bring it to a steady boil. Keep stirring to avoid the oysters from sticking to the bottom of the pan.
Cover the saucepan with a lid and allow it to simmer slowly on medium to low flame. Now, keep a close watch on the liquid and while you may not stir it as often, make sure that the liquid simmers steadily. Adjust the heat as per the requirements.
Take down the saucepan from the stove and add salt as per your taste. Stir the liquid well.
Use a strainer to sieve the contents from the saucepan.
Pour the oyster liquid into a saucepan. Add the soy sauce to the mixture. You will need almost 4 tbsp of light soy sauce followed by 1 tbsp of dark soy sauce. A mixture of the two will give the oyster sauce the right amount of depth of flavor. If you're not sure about the quantity of soy sauce to use, start by adding a little at first and gradually add more depending on your taste.
Meanwhile, you can either discard the oyster or use it later. If you want to use it, transfer it to a glass container with an airtight lid. Keep it in the refrigerator and try to use it within 4 days.
Going back to the recipe, keep the saucepan on the stove and allow the liquid mixture to come to a boil. Once it reaches a rolling boil, reduce the heat to medium-low and continue to cook it for 10 minutes
Keep the lid off the saucepan and allow the mixture to thicken as the liquid continues to simmer. The thickening process will be affected if the lid is kept on. Once done, allow it to cool before using it. If you don't wish to use it right away, pour it into a glass container with an airtight lid and refrigerate it.
If you wish to make the process quick, you can simply add the canning juice from a can of shucked oysters and discard the oysters at the start itself.
For the vegan/vegetarian version of the sauce, you can use sesame oil and ginger to saute a mixture of dried shitake mushrooms and flax seeds as a replacement of the oysters.