Add all ingredients *except* for the black salt to a small saucepan and whisk together until cornstarch is dissolved.
Heat over medium-high until it starts to boil. Reduce heat to low/medium-low and allow to cook for 2-3 minutes, whisking constantly, until thickened.
Remove from heat and whisk in black salt.
Enjoy drizzled over pan-fried tofu, or as a dipping sauce for toast. You may wish to sprinkle a little extra black salt on top, for extra eggy aroma.