Method:
1. Line a tart pan with the pie crust.  Chill while cooking vegetables.
2.  Peel and slice onions in half from root end to blossom end.  Place each half on cutting board and slice half circles that are 1/4" thick.
3.  Scrub mushrooms clean and then slice in 1/4" slices. 
4.  Place half of the butter and oil in large saute pan.  Add onions and saute on medium heat.  Cook until the onions caramelize.  This should take about 30 minutes or longer.  Stir occasionally.  Season with salt and pepper during cooking.
5.  In another saute pan, place the other half of the butter and oil.  Add the sliced mushrooms and saute until they are beginning to caramelize.  Season with salt and pepper during cooking.
6.  When both onions and mushrooms are just caramelized, combine them in one saute pan.  Add the chopped thyme.
7.  Remove from pan and let cool in a bowl.
8.  Once the veggies are cooled, add the gorgonzola crumbles.  Taste and adjust seasonings if necessary.
9.  Place cooled veggies in tart shell lined with crust.
10.  Place in a preheated 350 degree F oven. 
Bake for 30 minutes.  It will be necessary to cover it with foil for the last half of cooking to prevent drying of the veggies.
11.  Cool and cut.