Spread chicken on a cutting board or baking sheet, cover with plastic wrap, and pound with a Meat Mallet until chicken breasts are thin, even pieces. Sprinkle both sides with salt & pepper.
On medium heat, cook chicken in 1 T of cooking oil in a medium-large pan for 1 minute on each side. Reduce heat to low, cover (so pan is sealed shut), and let chicken cook for 10 minutes. Then turn off the heat and let the chicken cook, covered, 10 more minutes. Uncover and make sure chicken is no longer pink.
Meanwhile, melt butter in a separate medium-sized pan. Add shallot and garlic, and cook for a few minutes. Then, add mushrooms and cook for 5 minutes. Mix flour into vegetable mixture until evenly distributed and then pour in marsala wine (or grape juice), chicken stock and peas. Simmer for 10 minutes. Add milk/cream as final step and let sauce thicken for a couple minutes on low heat.
Add chicken to pan of sauce and simmer for a few minutes.
Video
Notes
To plate...sprinkle with parmesan cheese and serve! Feel free to serve with some sliced cucumbers and halved cherry tomatoes on the side.
Chicken tenderloins will cook faster than chicken breasts.
Instead of rinsing mushrooms, wipe or pat them with a damp paper towel. This prevents them from absorbing too much water.
Make sure your Marsala wine is dry or semi-sweet...not sweet.
If you don't have Marsala wine, you can use Sherry or grape juice, which is an excellent non-alcohol substitute for the wine.
For the sauce, milk, half & half, and cream will all work. The choice is yours.