1. Season the fillets well with salt and pepper. Place a large frying pan over high heat. Add the olive oil and the Salted Butter to give the dish aroma and flavor. When the Salted Butter has melted, place the chicken pieces skin-side down in the pan. Sauté the chicken over medium-high heat for 5 minutes. Flip to the other side and continue cooking for another 5 minutes, until golden brown. Remove the chicken from the pan and keep it warm.
2. Add the onion to the pan and sauté for 2-3 minutes. Add the garlic and stir for a few seconds. Pour in the wine and let the alcohol evaporate. Add the heavy cream, milk, lemon zest, and fresh oregano leaves, and stir. Bring to a boil and add the lemon juice, mustard, and the remaining salt. Stir, and once the sauce is boiling, return the chicken to the pan.
3. Simmer over medium heat for 5 minutes on each side, or until the chicken is cooked through and the sauce has thickened. Serve the chicken hot with mashed potatoes. Drizzle with the lemon sauce and garnish with fresh oregano leaves.
