Cut the nagaimo into thick semicircular slices. Microwave until tender enough for a skewer to be inserted easily (at 700 W for 1 minute and 40 seconds). Cut the bacon and Chinese cabbage into bite-sized pieces.
Make the white sauce. Put the butter in a pot over a medium heat and melt. Add the strong flour and sauté over a low heat.
When the butter and flour mixture become smooth, turn the heat off. Add the milk in one go and stir constantly over a low heat until smooth and thickened to the desired consistency.
Season with salt and sugar (this makes about 300 g of white sauce).
Melt some butter (not listed in the ingredients) in a frying pan. Fry the bacon and Chinese cabbage quickly. Add the nagaimo and mix all together. Season with salt and pepper (not listed in the ingredients).
Turn the heat to low and add Step 4. Bring to the boil quickly and then turn the heat off.
Transfer to a oven-proof dish and sprinkle with pizza cheese. Bake in an oven toaster until the top is golden brown.
Story Behind this Recipe
My son doesn't like Chinese cabbage. I made this recipe to get him to eat Chinese cabbage without his knowledge. Children love gratin dishes. You can sprinkle minced Japanese leek with the pizza cheese to taste. He wouldn't know there are vegetables he doesn't like in the dish. Nagaimo becomes fluffy when cooked. You can enjoy a different texture.
Do not overcook the Chinese cabbage and nagaimo to ensure they still retain their good texture. This white sauce is my own recipe. If you find it too runny add more butter and flour.