How to Make It
Preheat the oven to 425°. Season 4 of the chicken thighs with salt and pepper and lay them boned-side up on a plate.
In a small skillet, melt 1 tablespoon of the butter in 1 tablespoon of the olive oil over moderate heat. Add the onion and cook, stirring frequently, until translucent, about 5 minutes. Add the garlic and cook, stirring, for 1 minute.
Cut the remaining chicken thigh into 1/2-inch pieces and transfer to a mini food processor. Add the egg white and pulse 12 to 15 times, until the chicken begins to form a ball. Scrape into a small bowl and add the sautéed onion and garlic and the bread crumbs and parsley; mix well.
Using lightly moistened hands, spread one fourth of the stuffing on each seasoned chicken thigh to within 1/2 inch of the edge of the meat. Gently roll up the thighs; the stuffing should hold the rolls together.
In a medium, nonstick, ovenproof skillet, melt the remaining 1 tablespoon of butter in the remaining 1 tablespoon of olive oil over moderate heat. Add the stuffed chicken thighs, cover and cook until well-browned on the bottom, about 5 minutes. Turn the thighs and cook until browned on the second side, about 2 minutes longer. Sprinkle the capers around the chicken and roast uncovered for 15 to 20 minutes, until a thermometer inserted in the center of the thighs registers 150°. Transfer the chicken and capers to plates and serve.
Mashed Yukon Gold potatoes.