Cut the onion into thick slices.
Cut the potatoes and carrot into bite-sized chunks.
Cut off the base of the shimeji mushrooms and separate them.
Cut the chicken into bite-sized pieces.
Season the chicken with salt and pepper, then stir-fry until the color changes.
Add the vegetables and stir-fry until coated with oil.
Add the water, cover, and simmer over medium heat for 15 minutes.
Turn off the heat and dissolve the roux.
Simmer over low heat for 5 minutes.
Add the milk and Worcestershire sauce, then simmer for another 5 minutes.
Serve over rice.
