In a medium saucepan set over high heat, bring 2 cups of Marsala wine, gelatin, and shitake mushrooms to a boil. Reduce heat to medium and simmer until reduced by half, about 7-9 minutes.
2 cups dry Marsala wine, 4 teaspoons unflavored gelatin, 3 ounces Shitake mushrooms
While the sauce reduces, cut each chicken breast into 3 pieces: first halve the breast crosswise and then halve the fatter, remaining piece lengthwise. There should be 3 cutlets of similar size. Place cutlets between sheets of plastic wrap and pound each to ½-inch even thickness. Place all the cutlets in a large bowl and sprinkle with 2 teaspoons kosher salt and ½ teaspoon freshly ground black pepper. Set aside 15-20 minutes.
4 boneless, skinless chicken breasts, 2 teaspoons kosher salt
Pour the Marsala sauce through a fine-mesh strainer set over a medium bowl. Press on the remaining solids to extract as much liquid as possible and discard the solids. Pour the liquid back into the saucepan, add broth, and bring the mixture to a boil over high heat.
2 cups low-sodium chicken broth
Immediately reduce the heat to medium and simmer for about 15-20 minutes or until reduced to 1½ cups; set aside.
Place a wire rack in a rimmed baking sheet. Place the flour in a shallow dish and dredge cutlets (one at a time) in the flour – be sure to shake off any excess flour. Place cutlets on the prepared wire rack.
¾ cup all-purpose flour
In a 12-inch skillet, set over medium heat, heat 2 tablespoons oil just until smoking. Carefully, place 6 cutlets in the skillet and cook, without moving the cutlets, until golden brown, about 3 minutes. Flip the cutlets and cook until golden brown on the second side, another 2-3 minutes.
13 teaspoons vegetable oil
Set the cutlets back on the wire rack and repeat the process with 2 additional tablespoons of oil and the remaining 6 cutlets.
Set the now empty skillet to medium-low heat and add pancetta. Cook until the pancetta is brown and crispy, about 4 minutes, scraping the pan often to loosen any tasty bits stuck to the bottom of the pan.
3 ounces pancetta
Add the cremini mushrooms and cook, stirring and scraping the bits off the bottom, until the mushrooms have released their liquid and begin to brown. Cook until the liquid evaporates, about 7-9 minutes.
1 pound cremini or button mushrooms
Use a slotted spoon to transfer the mushroom/pancetta mixture to a small bowl; set aside.
Set the skillet over medium-low heat and add the remaining 1 teaspoon of oil and the shallot. Cook for about 1 minute to soften the shallot. Add the tomato paste and garlic, stir, and cook for about 30 seconds to bloom the garlic.
1 shallot, 1 tablespoon tomato paste, 1 clove garlic
Add the reduced Marsala mixture, dry sherry, lemon juice, and oregano. Bring to a simmer and add the chicken. Simmer for 3 additional minutes, flipping after 1½ minutes. Set the cutlets on a serving platter.
¼ cups dry sherry wine, 2 teaspoons fresh lemon juice, 1 teaspoon minced fresh oregano
Remove the skillet from the heat and whisk in the butter. Add the parsley and cremini mushroom/pancetta mixture. Taste and season with additional salt and pepper, if needed.
3 tablespoons unsalted butter, 2 teaspoons minced fresh parsley
Spoon the sauce over the chicken and serve over a bed of noodles or rice or mashed potatoes.