This slightly, or perhaps very, obscure way of cooking chicken breasts is based on the recherché restaurant technique of cooking sous-vide. This is the rustic take on the method, which, when you do it properly, involves a water bath maintained at a temperature a little higher than you might want to bathe in. The idea is that the meat or fish is poached very, very slowly, and then finished in a frying pan, giving you the best of both worlds: an exceptionally tender and succulent interior without sacrificing the crisp outside. — Anne Bell, Low Carb Revolution : Comfort Eating for Good Health.
Heat a tablespoon of oil in a large frying pan, add a pile of spinach leaves (you will need to cook them in batches), and toss until they wilt. Transfer them to a bowl and proceed with the remainder.
Lay the chicken breasts skin-side down on a board, flatten them with your hands, and cut out the white tendon from the underside, if visible.
Bring the stock to a boil in a medium-large saucepan and season with salt. Turn the heat down as low as possible. Immerse the chicken breasts in the stock and cook for 15 minutes, without boiling. Transfer them to a plate and pat dry with paper towels. The stock can be used again: first pour it through a fine sieve, discarding any sediment in the base.
Heat ½ tablespoon of oil in a large frying pan over medium heat, season the chicken breasts well, and cook for several minutes on each side until golden. You may need to do this in batches, or use two pans.
Just before the chicken is ready, heat a tablespoon of oil in another frying pan over medium heat, add the garlic and chile, and cook briefly until fragrant and lightly colored, then stir in the spinach, season with salt, and heat through. Serve the chicken and spinach accompanied by lemon wedges.