Cut asparagus on the diagonal into 1-2 inch pieces. Blanch for 5 minutes in boiling water. Drain and set aside.
Wash and slice mushrooms. Set aside.
Mince the garlic.
Rinse the black beans well. Mix garlic and beans together. Set aside.
Mix together the rice vinegar, tamari, starch, sugar, and sake. Set aside.
Fill a glass with water and set handy next to the stove.
Put a skillet over high heat. When the pan is hot, dump the garlic mixture into the pan. Stir fry for one minute,adding water as the mixture begins to stick add just a little at time.
Add the asparagus and stir fry for 10 minutes (or until asparagus is just shy of being crisp-done), again adding water just as needed.
Add mushrooms and stir fry for 2-5 more minutes.
Add the vinegar mixture (giving it a last stir to make sure starch is well mixed),stir until evenly coated and sauce thickens.