Roast the Pasilla Peppers under your broiler. Place the peppers on a foil lined sheet pan and position the sheet pan as close to your broiler as possible for about 5 minutes. Take the pan out of the oven, flip the peppers over and roast the other side for another 5 minutes.
Heat the butter and oil in a Dutch oven. Place the chicken in the Dutch oven and season with Salt and Pepper. Cook until browned then remove the chicken from the Dutch oven and set aside
Place the mushrooms in the Dutch oven and lightly brown them until golden. Remove to the same plate as the Chicken
Deglaze the Dutch oven with 1/3 cup of Dark Beer. Add the Onions, Garlic, Habaneros, Oregano, Cumin and allow them to sweat until the Onions are translucent
Whisk in the flour. Stir in the Chicken Stock then use an immersion blender to puree till smooth
Add the Pasilla peppers, Chicken, and Mushrooms to the pot. Cover and simmer for 45 minutes. Stirring occasionally