5teaspoonsdried mushrooms such as oyster or porciniground into a powder
1/2teaspoonfreshly ground black pepper
2cupscooked white rice
1 ¼cupsshredded cheese such as Monterey jack or cheddar
Preheat oven to 375° F.
Cut the peppers in half and remove the seeds and ribs. Lay the peppers cut side up in a 9 X 13 inch pan with 1/4 cup water in the bottom. Lightly sprinkle with kosher salt and microwave the peppers for 8-10 minutes until softened. Drain the water from the pan and set aside.
In a large skillet or dutch oven, sauté onions and celery with 1 tablespoon olive oil and a pinch of kosher salt over medium heat until they begin to soften, about 4-5 minutes. Add the cremini mushrooms and cook for another 5-7 minutes until the mushrooms soften then transfer to a bowl.
In the same dutch oven or skillet, melt the butter over medium heat, scraping bits from bottom of pan if there are any. Whisk in the flour and cook over low heat for 2-3 minutes, stirring constantly so flour taste cooks out and the mixture becomes lightly browned. Add the chicken stock and the milk to the butter and flour mixture, stirring constantly to avoid lumps. Add the thyme, crushing it between your fingers, the ground mushroom powder and season to with the salt and pepper. Bring the mixture to a boil then reduce to medium heat and cook until the sauce thickens and reduces by one third. Add the mushroom mixture back to the pan with the chicken and rice and cook until warmed. Add more milk if the sauce is too thick.
Lightly salt (about 1/4 teaspoon) the inside of the stemmed and seeded peppers and place in a microwave safe bowl with ½ cup or so of water, cover and cook for 5 minutes until starting to soften.
Place peppers in a 9 X 12 baking dish, skin side down, and fill pepper cavities with chicken mixture and top each pepper with a small handful of shredded cheese. Add extra filling around the peppers. Cover with foil and bake for 20 minutes or until bubbling and the cheese is melted. Rest for 5 minutes and serve.