i made these into stuffed mushroom appetizers and i still didnt use up all the filling with 10oz of baby bellas.  it was really good though, i sauteed the garlic and shallots with the stems before mixing them and then i drizzled the finished product with the mayo mixture.  I've been dipping chips and pretzels into the leftover filling - yum.

this recipe was great! I changed it up a bit, as others did. Instead of the mayo, I marinated the mushroom in some balsamic vinegar & olive oil, then cooked it over the stove, instead of in the oven. & since people were saying the cream cheese mixture was really good, i decided to have the whole thing on a bagel. it made a very delicious dinner :-) 

 >>>Yummy! I loved this, it was so decadent! The only changes I made were adding sundried tomato's and 1tbs nutritional yeast to the cream cheese mixture, topping it off with green onions, and cooking it closer to 40 min to get a nice brown color. So delicious, and the mixture made enough for three mushrooms. Thanks alot, this will become a staple in my house.

This was delicious! Some comments/suggestions made by others that I agree with:
a) saute the shallots and garlic (my stems were yucky so I didn't use them)
b) the filling was probably twice as much as necessary (it oozed everywhere) and next time I would make four burgers
c) broil the mushrooms at the end to brown the cheese (my idea)
d) I would almost rather just make stuffed mushroom appetizers but the balsamic dressing really made the burger Maybe it could be drizzled over the top?
So..... give this a try and play with it as you will. It is a messy, tasty treat!