Preheat oven to 425 degrees F.
Add onions. thyme sprigs and 1/4 cup oil to a saute pan and slowly saute for at least 30 minutes until you get a nicely browned/caramelized color. The thyme will fall off the sprigs so no need to remove it.
Add your mushrooms and garlic and saute for another 5 minutes.
Add the sherry wine and let simmer for 2-3 more minutes before taking off the heat.
If using pizza dough: Roll your dough out as this as you can without putting holes in it. Brush 1 tbsp. oil over top of the dough and season with salt/pepper. If using store-bought flatbread: Brush 1 tbsp oil over top of the dough and season with salt/pepper.
Bake dough/flatbread at 425 F for 10-12 minutes or until golden brown. (store-bought flatbread may brown quicker!)
Once your crust is nice a crispy. Remove from oven and spread the mushroom mixture evenly over top topping finishing with the cheese. Bake 5 more minutes or until melted. Cut into strips and serve warm!