Step 1

Trim and thinly slice 8 ounces baby bella mushrooms (about 3 cups). Mince 3 garlic cloves. Place 1/3 cup all-purpose flour in a large shallow bowl or pie plate.

Step 2

Cut 1 1/2 pounds boneless, skinless chicken breasts in half horizontally (also known as butterflying). For pieces larger than 1/4-inch thick, pound the chicken pieces: Working with 2 pieces at a time, place in a large resealable bag and pound to an even 1/4-inch thickness. Pat dry with paper towels. Season all over with 1 teaspoon of the kosher salt and 1/2 teaspoon black pepper. Working with 1 piece at a time, dredge the chicken in the flour, shaking off any excess.

Step 3

Heat 1 tablespoon of the unsalted butter and 1 tablespoon of the olive oil in a large (12-inch) stainless steel or cast iron skillet over medium-high heat until shimmering. Add half of the chicken in a single layer and sear until browned, 3 to 5 minutes per side. Transfer to a large plate (the chicken will not be cooked through). Add 1 tablespoon of the unsalted butter and the remaining 1 tablespoon olive oil to the skillet and repeat browning the remaining chicken. Transfer to the same plate.

Step 4

Melt 1 tablespoon of the unsalted butter in the skillet. Add the mushrooms and cook, stirring occasionally until they’re tender, release their liquid, and begin to brown, 4 to 5 minutes. Add the garlic and cook until fragrant, about 30 seconds.

Step 5

Add 2/3 cup marsala, 2/3 cup low-sodium chicken broth, and the remaining 1/2 teaspoon kosher salt. Scrape the bottom of the skillet with a wooden spoon to release any browned bits. Bring to a simmer. Return the chicken and any accumulated juices on the plate to the pan in a single layer. Cook until the sauce is slightly thickened and the chicken is just cooked through, 4 to 5 minutes.

Step 6

Remove the skillet from the heat. Add the remaining 1 tablespoon unsalted butter and stir until melted. Garnish with finely chopped fresh parsley leaves if desired.