Place chicken, garlic, sage and rosemary sprigs, juniper berries (if using), carrot, celery, onion, bay and wine in a shallow dish or plastic food storage bag. Seal or cover and marinate overnight.
Preheat oven to 400°F.
Pat chicken dry and strain the wine, reserve. Season the chicken with salt, coarse black pepper and chopped rosemary. Heat a large, heavy skillet over medium-high heat with 1 tablespoon olive oil, a turn of the pan. Brown the chicken thighs on both sides and remove to plate. Add 2 tablespoons more oil and melt 2 tablespoons butter into oil. Brush the bread with oil and butter on both sides, add the bread to pan and brown the bread on 1 side; turn. Top the bread with the chicken, 2 thighs per slice of peasant bread then pour the wine evenly overtop of the chicken and bread. Place in oven and roast 20 minutes.
In second skillet, heat 1 tablespoon olive oil, a turn of the pan, add spinach or chard and wilt, season with salt, pepper and nutmeg.
Serve chicken and bread with wilted greens alongside.