First, mix together ⅓ Cup of flour with 1 Teaspoon Salt and ½ Teaspoon Pepper to make a dredge.
Coat boneless skinless chicken thighs in seasoned flour.
Heat a large sauté pan or Dutch oven on medium-high heat and add olive oil.
Next, brown the coated thighs on both sides for about three minutes. Remove from the pan and set them aside.
Then, turn the heat down to medium-low, and add butter and sliced cremini mushrooms.
Let the mushrooms cook until they start to soften.
Then add diced onion and minced garlic. Season with salt and pepper. The salt will help draw out the moisture from the onions and mushrooms.
Cook until the onion is translucent.
Sprinkle a Teaspoon of flour over the cooking vegetables and let it absorb the fats in the pan.
Next, add dry marsala and balsamic vinegar to deglaze the pan. Use a wooden spoon to get the brown bits off the bottom of the sauté pan.
Bring the mushroom marsala sauce to a low simmer and let cook for 5 minutes.
Then, add the browned chicken thighs to the sauce and simmer with the lid on for 15 minutes.
Remove the lid, spoon some sauce over the chicken pieces and simmer uncovered for 5 more minutes.