Preheat oven to 350° F.
Melt butter in cast iron skillet. Add onion, mushrooms, and chicken paste. Saute for about 20 minutes, until onion and mushrooms begin to caramelize. If you prefer more caramelization, you may caramelize for up to 40 minutes.
Add sage, garlic, thyme, and pepper. Stir for one minute.
Add cream and nutritional yeast (optional) and stir occasionally at medium heat until thickened, about 5-10 minutes.
Stir in turkey, parsley (optional), and ¼ cup Parmesan cheese and remove from heat.
If using a non oven-safe skillet, pour ingredients into an oven-safe baking dish (an 8" x 8" dish should work).
Sprinkle mozzarella and remaining Parmesan on top.
Place skillet or dish into oven and bake at 350° F for 12-15 minutes, until bubbly and slightly golden. Garnish with more parsley, and serve.
