Saute your mushrooms and thyme in olive oil over high heat.
After 5 minutes, add your sherry wine to the pan and saute another minute until the alcohol cooks off.
Add in all your spinach and saute another minute or two until the spinach is slightly wilted. (Don't worry, it will cook down) Season with salt and pepper (to taste) and remove from heat.
Char both sides of your tortillas by placing them DIRECTLY over an open fire. You can use a grill or your stove top. (Set heat to medium). Keep a close eye so you do not burn them!
Add cheese to one side of charred tortilla. Then add ¼ of your spinach/mushroom mixture on top of the cheese. Lastly, sprinkle more cheese and close up your quesadilla. **Each quesadilla should have about ¾ cup of cheese split between top and bottom.
Assemble all 4 quesadillas and place onto two sheet pans (two on each). Bake at 350F for at least 5 minutes or until cheese is fully melted.
Allow to cool slightly before cutting. (I cut mine into 6 slices.) Top with sour cream and chives for garnish!
*Reheat your quesadillas in the oven for 2-4 minutes (after they have been cut) so you can serve to guests immediately while still hot.*Serve sour cream, guacamole, pico de gallo, etc. on the side so your guests can add what they want.