1. Sprinkle chicken breasts with 1/4 teaspoon salt, or as needed on both sides. Place onto a rack, cover, and refrigerate for 30 minutes. Remove from refrigerator and cut in half lengthwise on a slight diagonal to make 4 equal-size pieces. Place the chicken pieces between two sheets of heavy plastic (resealable freezer bags work well) on a solid surface. Firmly piund the chicken with the smooth side of a meat mallet to make 4 cutlets about 1/4 inch thick.

2. Preheat oven to 200 degrees F.

3. Mix together flour, cornstarch, 1 teaspoon of salt, black pepper, and sugar in a shallow bowl. Place each cutlet into the flour mixture to coat; shake off excess flour. Melt 2 tablespoons of butter in a skillet over medium heat until foam disappears, and gently lay the coated cutlets into the butter. Cook until golden brown on both sides, about 3 minutes per side. Remove the chicken, and set aside on an oven-proof plate in the preheated oven to stay warm.

4. Pour the sherry into the skillet and bring to a boil, scraping and dissolving all the brown flavor bits from the bottom of the skillet. Cook until the sherry is reduced to half its volume, about 5 minutes, and stir in the chicken broth; add the apple slices to the skillet. Cook, stirring occasionally, until the apples are soft and sherry mixture is reduced by half. Stir in the brown sugar, 1 tablespoon of butter, and the Marsala wine until the sugar is dissolved and the sauce is thick.

5 Return the chicken cutlets to the sauce, together with any juice from the plate, and turn to cover cutlets with sauce. Simmer about 2 minutes per side, and serve 2 cutlets per serving, topped with apple slices and sauce.