Heat the butter and half of the oil in a skillet. Brown both sides of the chicken breasts over medium heat.
Remove the chicken from the skillet, drain excess grease and de-glaze with the chicken stock, scraping the bottom with a wooden spoon. Add the chicken breasts to the stock, season with salt and pepper, lower the heat and cook covered for 5 to 6 minutes.
In another skillet, heat the remaining oil. Mix the onions, apples and leeks and cook until they begin to caramelize. Add the nutmeg, the yogourt and the juices reserved from the chicken and mix.
Divide the contents of the second skillet onto the plates, arrange the chicken in a fan shape and cover with the remaining sauce.
Per 408 g serving: 410 calories, 18 g total fat, 23 g carbohydrate, 39 g protein, 214 g calcium