Remove any excess fat from the chicken thighs.
Add the salt, onion powder and black pepper to a small bowl, stir to combine. Season the chicken on both sides with the seasoning mix.
Heat the oil in a large, deep skillet over medium heat. When the oil is hot, but not smoking add the chicken thighs, skin side down. Cook the chicken 5 minutes until the skin is nice and golden brown.
Flip the chicken and brown the other side, about 4 more minutes.
Remove the skillet from the heat and remove the chicken, place it on a plate or pan, keep it warm by covering loosely with a piece of aluminum foil, and/or place the plate in the microwave or oven.
Drain the any oil remaining in the skillet, but don’t wipe or wash.
Set the skillet back over medium heat, add the butter. When the butter is melted and foamy add the mushrooms and garlic cloves. Cook the mushroom and garlic gently for 5 minutes, stirring frequently.
Add the flour to the skillet and stir until well combined. Cook for 1 minute, stirring almost constantly
Add the chicken broth to the skillet, stir, scrapping bits off the bottom of the skillet gently as you stir. Bring the liquid to a boil.
Arrange the reserved chicken in the skillet, skin side up.
When the liquid comes back to a boil, lower the heat to medium-low and cover. Cook the chicken for 30 minutes, stirring the sauce occasionally. After it’s covered, keep the sauce at a simmer, if it’s boiling too vigorously, lower the heat a bit. Make sure the internal temperature of the chicken is at least 165°F at its thickest part.
Serve the braised chicken over noodles or mashed potatoes with a generous amount of the mushroom garlic sauce, and garnish with a little chopped parsley, if desired.