Raspberry Chicken

Recipe from: Sam and Katie's Favorite Recipes, 1992

Ingredients:
2 whole boneless, skinless chicken breasts (about 2 lbs)
2 Tbsp sweet butter (unsalted)
1/4 cup finely chopped onion
4 Tbsp raspberry vinegar
1/4 cup chicken stock or broth
1/4 cup heavy cream
3 Tbsp canned crushed tomatoes
16 fresh raspberries (optional)

Directions:

1. Cut each chicken breast into halves along the breastbone line. Flatten each breast half by pressing it gently with palms.
2. Melt butter in a large skillet. Raise the heat, add chicken, and cook for about 3 minutes per side, or until lightly colored. Remove from skillet. 
3. Add onion to the pan and cook, covered, over low heat until tender, about 15 minutes.
4. Add the vinegar, raise the heat, and cook, uncovered, stirring occasionally, until vinegar is reduced to a syrupy spoonful. Whisk in chicken stock, cream, and tomatoes and simmer for 1 minute.
5. Return chicken to skillet and simmer, basting often with sauce, until they are just done and the sauce has been reduced and thickened slightly, about 5 minutes. Be careful not to overcook. 
6. Remove chicken from sauce and arrange on a heated serving platter. Add raspberries to the sauce and cook over low heat for 1 minute. Pour the sauce over the chicken and serve immediately.