Mix the chicken stock with the shiitake mushroom stock in the stockpot then add the sliced shiitake mushrooms. Place the stockpot over medium-high heat. Once the stock starts to boil, reduce the heat to keep the stock simmering.
Scoop tablespoonfuls of meat mixture with one spoon and use a second spoon to shape into balls.
Gently drop the meatballs into the simmering broth, one at a time.
Cook the meatballs for 1 minute then add the cabbage, carrot, and cremini mushrooms.
Cover the pot with a lid and allow the hot pot to cook for about 5 minutes. If needed, adjust the heat to maintain the stock at a gentle simmer.
When the vegetables are cooked through and the meatballs are no longer pink in the center, turn off the heat.
Season the hot pot with black pepper and serve.