grifola frondosa

Also known as the maitake.  I thought I had never had one before but they are also called Hen of the Woods.  And I have indeed had those.  I spotted them at our local Asian grocery store, Mitsuwa.  I declare it the best mushroom ever.  The bacon of mushrooms.

The Wikipedia entry also has some interesting facts:

• It can grow to 50 lbs in weight.
• Medical research has shown that it stimulates the immune system
• Medical research has shown it can inhibit cancer cells
• It has a hypoglycemic effect.  So it's an Atkin's superfood.  It not only has very little carbohydrate but it has a calming effect on your insulin response. 

Note to self:  Buy more maitake.