3 tablespoons extra virgin olive oil
1/4 cup raisins
1/4 cup pine nuts
1 tablespoon minced garlic
1 pound fresh spinach leaves
Salt and freshly ground black pepper
1/4 cup panko (Japanese bread crumbs), optional
4 boneless chicken breasts (about 11/2 pounds)
2 tablespoons balsamic vinegar
1 tablespoon Dijon mustard

Preheat oven to 350 degrees. Cut six 8-inch pieces of butcher twine. Put 2 tablespoons olive oil in a large ovenproof skillet over medium-high heat. When hot, add raisins, pine nuts and garlic, and cook for about 30 seconds; add spinach, sprinkle with salt and pepper, and cook, stirring constantly, until wilted and fairly dry, about 10 minutes. Remove and roughly chop; stir in panko, if you like. Set skillet aside.

Spread out two chicken breasts on a work surface so that the sides where the bones were face up. Flatten them a bit with your palm, a rolling pin or the bottom of a pot. Place stuffing on top, then top with remaining breasts, end to end, the thick side of the top breast on the thin side of the bottom one, so the ‘’sandwich’’ is of fairly even thickness. Tie each stuffed breast in three places with twine.

Sprinkle all sides with salt and pepper. Use remaining tablespoon of olive oil to brown chicken in skillet used for spinach. Transfer to oven and bake, turning once, until chicken is cooked through and opaque, 25 to 30 minutes.

Remove chicken from skillet and tent with foil. Set skillet over medium heat and add vinegar, mustard and 2 tablespoons water. Cook, stirring frequently, until sauce is a thin syrup. Add a few more grinds of black pepper. Remove string from chicken and slice crosswise into thin or thick pieces. Serve with a spoonful of sauce drizzled over all.