Cauliflower, Caramelized Onion and Mushroom Tart

A smittenkitchen recipe.  I just added mushrooms to the mix because I had mushrooms I needed to use up much to my friend Allison's dismay.

I also did not have Gruyere cheese and I'm not a fan of Swiss cheese so I just left that out.  I may have used mozarella to top one of the tarts (I made two of these) and it really doesn't make a huge difference.