You can use anything for stuffing — I first used reconstituted and sauteed porcini, dried tomatoes, olives and bread crumbs. Later I used kale, but settled on spinach with garlic, pine nuts and raisins. Reconstituted dried fruit would be nice, though so might sliced plums or even fresh tomatoes or peaches (with chopped basil in the pan sauce.) Intense flavors are good, since there’s not room for too much. Whatever you use, it should be about 1 cup packed total (or 1/2 cup per roll).
This recipe is nice because you don't have to cut a pocket, or pound the chicken — just tie it. Plus this method just requires one skillet. Finally, note: You can of course serve the chicken and greens separately, but the stuffed chicken is nice and fancy.
1. Heat the oven to 350 degrees F. Cut six 8-inch pieces of butcher twine. Put 2 tablespoons of the olive oil in a large ovenproof skillet over medium-high heat. When hot, add the raisins, pine nuts and garlic and cook for about 30 seconds. Add the spinach, sprinkle with salt and pepper, and cook, stirring constantly, until wilted and fairly dry, about 10 minutes. Remove and roughly chop; stir in the panko crumbs. Note: Be sure to cook filling first, because it won’t cook inside the chicken and you want it to be fairly dry.
2. Spread two chicken breasts out on a work surface so that the side where the bones were is face up. Flatten them a bit with the palm of your hand. Put the stuffing on top of the two breasts, then top with the remaining breasts, end to end, so that the tapered side is on the same side as the rounded side (this ensures a tidy roll and even cooking). Tie each stuffed breast in three places with twine. Sprinkle all sides with salt and pepper and roll them around in the same pan you used to cook the spinach, adding another tablespoon of olive oil to coat them well. Transfer to the oven and bake, turning once, until the chicken is cooked through and opaque, 25 to 30 minutes.
3. Make a quick pan sauce while the chicken is resting: Remove the chicken from the pan and tent with foil. Set the pan over medium heat and add the vinegar, mustard and a little water. Cook, stirring frequently, until the sauce thickens into a thin syrup. Add a few more grinds black pepper. Remove the string from the chicken and slice crosswise into thin or thick pieces. Serve with a spoonful of the sauce drizzled over all.