Finely chop the onion. Remove the stems from the maitake mushrooms and cut into bite-size pieces together with the king oyster mushrooms. Put in a bag with flour and shake to coat in flour.
Melt butter in a pan and heat the onions. Add the mushrooms from Step 1 and cook. When the powder is gone add the sake, salt and pepper, and garlic.
Reduce to low heat and add 1/3 of milk and mix well. When it's smooth, add the remaining milk and slightly increase the heat, mixing well. Adjust the flavor with salt and pepper.
Cook until the mixture obtains a creamy thickness; it should slide slowly as you tilt the frying pan. At this point, add the drained pasta and mix well to complete the dish.
Boil the water. Add salt to the water, then boil the pasta. This is just a guideline.
Please boil the pasta for 3 - 4 minutes shorter than what's listed on the package. If you are going to add the sauce after placing the pasta on a plate, then cook as directed.
Boiling time for the pasta will vary depending on the pasta type. Try to time the sauce to go together with the pasta.
If you don't have confidence timing, first boil the water. Make the sauce, and then boil the pasta.