Heat a large skillet on medium-high. Add in a thin layer of oil.
In batches, brown pork cubes.
When all the pork is browned, combine with stock, soy sauce, sugar, sake, mirin, garlic and ginger.
Bring to a boil and simmer until the pork is tender. This can take 2-3 hours.
Pork is done when the pieces are easily pierced with a fork. (Take care not to go too long or the pork will fall apart)
Remove the pork pieces and reduce the liquid until slightly thickened and glossy.
Add the pork back and serve.
