1Pre-heat over to 300 degrees. You will not need to grease or spray your baking dish as they will produce their own oil during cooking process.
Wash mushrooms and pat dry with paper towel. Using a sharp knife cut out (or pop out) the stem piece and center of mushrooms. (I chop these and reserve for another recipe or later use).
2In medium mixing bowl place softened cream cheese. Add 1/2 of Mozerella and 1/2 of Cheddar. Slightly mix this and microwave on low cook power till cheese begins to melt. Remove from microwave and immedately add sour cream and mayo. Mix well quickly and then add remaining ingredients. Mix well again.
3Fill and overfill each mushroom cap with the ingredients above. (It's ok if some of the mixture is on top of the mushrooms. Once you have completed all mushrooms, sprinkle the remaining shredded mozerella and cheddar on top of all.
4Bake for approximately 20 minutes until cheeses are browning and bubbly. Remove from oven and immediately place each mushroom carefully on a serving platter with a curved lip or sides as oil will still be produced. (Take all of the melted cheese with you to the serving platter that has accumulated on bottom of baking dish! Yummy - enjoy!
*Note - They look exceptionally nice in serving dishes available at some of the kitchenware stores. They are oblong and narrow - approximately 10 x 2 x 2. You could use several of these to place at different locations on your dining table to keep from being passed around.