Make a salt solution by dissolving 1 tbsp of salt into 6 cups of water.
Add one cup of salt solution (reserve the rest for later use), the shucked oysters, and the liquid from the shucked oysters into a sauce pot. Then bring it to a boil and simmer for 5 minutes.
Pour the cooked oyster&water through a sieve and collect the liquid into a big pot.
Put the cooked oysters, shallot, ginger, scallion, garlic, and 1 cup of salt solution into a powerful blender. Blend into a puree.
Pour the oyster puree into the saucepot and simmer for 5 minutes. Then let it go through a fine cheesecloth with a big pot to collect the liquid.
Rinse the blender and the sauce pot with 1 cup of the salt solution, then pour it through the cheesecloth; this helps to cool down the oyster puree so you can squeeze it with your hand.
In batches, continue to rinse the oyster puree with the rest of the salt solution. Stir well and squeeze the cheesecloth until no more liquid comes down. Discard the solid part of the oyster.
Simmer the big pot of oyster liquid over medium-low heat for 1-1.5 hours or until 1/3 cup of liquid is left. You don't need to babysit the pot the whole time, but keep an eye on it to prevent burning.
While waiting, heat the sugar in a saucepot over medium-low heat. Stir for 6-8 minutes or until all the sugar is melted and the color turns golden brown. Pour in 2 cups of water and bring to a simmer to dissolve the caramel. Turn off the heat and remove it to the side.
Check back the oyster liquid. Once you have 1/3 cup of liquid left, turn the heat to the lowest and stir for 5-8 minutes or until the liquid turns into a brown sticky paste. This is what we call oyster concentrate, which is too flavorful to cook with.
Add the caramel solution to the oyster concentrate in batches and stir thoroughly to dissolve.
Season oyster caramel solution with salt, dark soy sauce, and MSG; then bring it to a simmer. Add the cornstarch water in batches and stir until the sauce thickens.
Store the oyster sauce in clean, sealable jars for two months in the fridge and 12 months in the freezer. Use this sauce for any recipe that asks for oyster sauce.