Cut mitsuba into 4cm lengths. Mince the shiitake mushrooms.

Place cabbage leaves in a microwave-safe container, cover loosely with plastic wrap, and microwave at 600W for 5 minutes. Drain and let cool. Flatten the thick stem parts and mince them.

In a bowl, mix breadcrumbs and beaten egg. Add the remaining meat filling ingredients, including the minced cabbage stems, and mix well until sticky. Divide into 4 portions and shape into oval patties.

Lay a cabbage leaf flat, place a meat patty slightly below the center, and wrap tightly. Repeat for all 4 rolls.

Place the cabbage rolls seam-side down in a pot. Add the seasoning ingredients and bring to a boil. Cover and simmer on low heat for 20 minutes.

Remove the cabbage rolls from the pot. Add the potato starch slurry to the pot and stir until the sauce thickens.