Cut onion, potato, carrot, and pork into bite-sized pieces.
Heat cooking oil in a pan and stir-fry the pork.
Add onion, potato, and carrot and continue stir-frying together.
Add black bean sauce and mix well with the ingredients, stir-frying.
Pour in water and simmer over medium heat until the ingredients are cooked.
When the potatoes are cooked, add starch water to thicken the sauce.
Serve the black bean sauce over rice to finish.