Thinly slice the onion. Remove the stem of the shimeji mushrooms and tear into small pieces with your hands. Cut the potato into 1-cm cubes. You can use anything you like for the ☆ ingredients.
Heat olive oil in a frying pan and fry the ingredients from Step 1 well. Cook the macaroni.
Sprinkle the flour into the frying pan from Step 2, and continue frying until it is no longer floury. Then add the soy milk and dissolve in the white miso. Simmer on a low heat until it starts to thicken.
Season with salt and pepper, add the cooked macaroni and stir. Pour into a heatproof dish.
Top with cheese and panko to your liking. Bake for about 15 minutes in a 220℃ oven, and it's done when the cheese has melted.
You could substitute the ☆ ingredients with whatever ingredients you like. This is made with onion, spinach, mushroom, and boiled egg. I topped mine with boiled eggs before adding the cheese.
It's also great with onion, mushroom, and small shrimp. In my house, we like to use two different types of cheeses, or make it without any cheese at all.
If you are using stock cubes instead of white miso, just add a little bit of salt. I use these bouillon stock cubes shown in the photo.
Story Behind this Recipe
I love gratin, but I'm trying to avoid meat products...so I just used cheese.
If you want to make this completely vegetarian without cheese, you can top it with panko breadcrumbs in Step 5 and bake. You could also add cooked pasta in Step 4 and make it cream spaghetti. It's also tasty if you add 2 bowls of rice in Step 4, and carry on to Step 5 to make it into rice gratin (doria).