Bring the water to a boil and add the ancho chilies before moving the pot off of the heat. Allow the chilis to soak for 30 minutes before removing from them from water, cutting off the stems, and scraping out the seeds. Reserve 120ml of the water.
Add the reserved water, de-seeded ancho chillis, and 4 of the garlic cloves to a blender and blend until smooth.
Preheat the oven to 180c/160 fan. Heat a large pan or skillet over medium heat and whisk the purée, double cream, and sour cream together. Reduce to a simmer and whisk in the lime juice and salt to taste.
In a large skillet add the oil over medium heat. Once hot, add the the onions and cook for about 2-3 minutes until translucent. Add the garlic for one minute before adding the mushrooms and Mexican oregano. Cook the mushrooms for about 5 minutes before adding the tomatoes, 125ml of the ancho cream sauce, and 40g cheese. Stir to combine and simmer until the mixture is heated through. Season with a few grinds of fresh black pepper and salt to taste.
Grab a 24cm square pan and build your dish similar to a lasagna. I cut four tortillas per layer in half to place as half moons around the edge of the pan, and have one full tortilla in the middle. Put a layer of of the sauce at the bottom of your dish (about 1/2 cup or 120ml), followed by a layer of tortillas, a layer of mushrooms, and more cheese. Continue this layering process until you have three layers. Make sure that your top layer is finished with the last of the sauce and generous cheese. If you want less heat in your dish, you can use less of the ancho cream sauce.
Bake in the oven for 20 minutes. Allow the dish to rest for 10 minutes before serving with avocado, sour cream, and fresh coriander.