First do the prep-work. While the macaroni is boiling, mince the onion along the grain. Remove the stem ends from the shimeji mushrooms and separate. Cut the bacon into 1 cm thick slices. Cut the cheese into 2 cm cubes.
Cook the onion, shimeji mushrooms, and bacon in an oiled frying pan. Flavor with salt and pepper, and once the onions wilt add the butter and melt. Then add the flour, and cook until no longer floury. Then add the milk to create the white sauce.
Add the cheese to the finished white sauce and dissolve. Once it's dissolved add the macaroni. If you like you can bake for about 10 minutes in an toaster oven to make it aromatic. But it's still plenty delicious unbaked as well.
Story Behind this Recipe
I love cheese, so I tried making this with cheddar cheese, which I usually have in stock.
You can use whatever cheese you like, but I think cheddar is best. For the macaroni, I think it's best to use something with groves, to make it easier to mix in with the sauce.