Gather all ingredients.

Pour milk into a wide, shallow bowl. Spread flour into a separate wide, shallow bowl. Dip each chicken breast half into milk to coat; move to the dish with flour and press chicken into flour to coat entirely.

Heat oil in a skillet over medium-high heat. Fry chicken in hot oil until golden brown, about 3 minutes per side. Remove chicken to a plate; drain fat from the skillet and return to medium-high heat.

Melt butter in the skillet. Sauté mushrooms in hot butter until softened, about 2 minutes.

Pour white wine over mushrooms. Stir gravy, half-and-half, and mustard with mushrooms; season with salt and pepper. Bring the liquid to a simmer and cook for 2 minutes.

Return chicken to the skillet and cook until chicken is no longer pink in the center and juices run clear, about 5 minutes. An instant-read thermometer inserted into the center should read at least 165 degrees F (74 degrees C).