For filling: Drain the tomatoes, reserving 2 tablespoons oil. Finely chop tomatoes. In a medium skillet, cook and stir tomatoes, mushrooms and pine nuts in reserved oil from the tomatoes over medium heat for 4 to 5 minutes or until mushrooms are tender and most of the liquid has evaporated, stirring occasionally. Remove from heat; set aside.

Place a chicken breast half between 2 pieces of plastic wrap. Using the flat side of a meat mallet, lightly pound chicken into a rectangle about 1/8 inch thick, working from the center to the edges. Remove plastic wrap. Repeat with remaining chicken breast halves. Sprinkle with salt and pepper.

For each roll, place one-fourth of the mushroom mixture in center of chicken piece. Sprinkle with one-fourth of the feta cheese. Fold in the sides of the chicken breast half and roll up. Press all edges firmly to seal in the filling. Secure with wooden toothpicks, if necessary. Repeat with remaining chicken, filling and cheese. Place rolls, seam side down, in a shallow baking pan.

Bake, uncovered, in a 375 degree F oven about 30 minutes or until chicken is no longer pink (170 degree F). Meanwhile, prepare sauce.

For sauce: In a heavy small saucepan, melt the 2 tablespoons butter. Stir in flour, 1/8 teaspoon salt and 1/8 teaspoon pepper. Cook and stir over low heat until evenly combined. Remove from heat. Transfer to a small bowl. Add whipping cream and stir until well combined; set aside.

In same saucepan, melt the 1 tablespoon butter. Add onion. Cook and stir for 2 to 3 minutes over medium heat until onion is tender, but not brown. Add balsamic vinegar. Cook and stir until slightly thickened, about 2 minutes. Add chicken broth; bring to boiling. Reduce heat. Simmer, uncovered, for 15 minutes, stirring occasionally. Whisk in flour/whipping cream mixture. Cook and whisk over medium heat until thickened and bubbly. Cook and whisk for 1 minute more.

Remove toothpicks from chicken, if using, and transfer to a serving platter. Serve sauce with chicken. Makes 4 servings.