Let's cook the cabbage. Insert the blade of the knife along the core, and remove it from the cabbage. Removing the core at this stage makes it easy to separate each leaf later.
Place the cabbage in a bowl and cover it with 2 sheets of plastic wrap crosswise.
Microwave the cabbage at 600 watts for 10 minutes. Then, flip it over and cook for 5 to 6 more minutes. If the cabbage is still firm, microwave it for 3 more minutes at a time. Leave the cabbage in the microwave for about 5 minutes and remove.
Now, the bottom of the cabbage should be soft as shown. Carefully detach each leaf to avoid breaking it. If some soil remains on the surface, lightly rinse it away.
Remove the moisture with a clean kitchen towel.
Trim off the firm stalk. Place the cabbage leaves onto a tray.
Repeat the process until you have 17 leaves. The cabbage we used is 1.6kg (3.5 lb), but even if your cabbage is 1.2kg (2.6 lb), you should be able to get at least 17 leaves. You can use the remaining cabbage in gyoza filling or vegetable soup.
Let's make the meat filling. Add the milk to the panko, Japanese breadcrumbs. Stir to combine. Then, let it sit for about 1 minute.
Next, place the ground beef and pork in a bowl and add the salt and pepper. With your hand, squish the meat to mix.
Add the panko moistened with milk and egg. Squeeze the mixture to combine all the ingredients.
Then, loosely spread your fingers forming a rake shape to thoroughly mix the meat until it turns gooey. This will help to combine the ingredients.
Add the chopped onion. Roughly mix and blend the onion with the meat.
Finally, divide the meat mixture into 8 portions.
Let's wrap the meat filling. With a rolling pin, pound the firm bottom part of the cabbage leaves to soften. This will make it easy to wrap the filling, but be careful not to break the leaves.
You will be using 2 leaves, both a small size and a large size, to make each cabbage roll. Place the smaller leaf on top of the large cabbage leaf, and spoon one-eighth of the meat mixture onto it.
Wrap the meat with the small leaf. The leaves may have some slits, but using 2 sheets of cabbage will help to wrap the meat tightly and evenly.
Next, cover it with the bottom part of the large cabbage leaf. Fold both sides of the large leaf.
Tightly roll the inner cabbage roll to avoid loosening. Even if the outer leaf breaks while cooking, the meat is still kept in the cabbage. Additionally, you can enjoy lots of cabbage, so we recommend wrapping it with 2 leaves.
Fasten the edge of the leaf with a bamboo stick. You can also tie the cabbage roll using a piece of long pasta.
With the closed side facing down, arrange all the cabbage rolls in a slow cooker. Avoid leaving gaps between the cabbage rolls. If there are spaces, the leaves will easily come loose while cooking so choose the size of the slow cooker or pot wisely.
Add the tomato sauce. Add hot water until the cabbage rolls are submerged.
Add the bacon strips, chopped bouillon cube and bay leaf.
Cover the ingredients with the last cabbage leaf, but you can skip this if there aren't any left.
Place a drop-lid on top and cover the slow cooker with a lid.
Cook on high heat for 3 hours until the cabbage leaves become tender.
Now, the cabbage has softened completely. Remove the covering cabbage leaf and bay leaf. After testing the sauce, adjust the taste with salt and pepper.
Using tongs, place 2 cabbage rolls onto a plate. Don't forget to remove the bamboo sticks.
Ladle the sauce over the cabbage rolls. Finally, sprinkle on grated Parmesan cheese and chopped parsley leaves.
You can also add finely chopped carrot and mushrooms to the meat filling, making a slightly different version quickly.
If you don't have a slow cooker, cook it in a heavy pot on low heat for at least 40 minutes to 1 hour.