In a large skillet over medium-high heat, melt 1 tablespoon of the butter. Season the chicken on both sides with salt and pepper, then add half of it to the pan. Cook for 3 minutes on each side, then transfer to a plate. Add the remaining tablespoon of butter and repeat with the remaining chicken. Transfer the second batch of chicken to the plate, cover with foil and set aside.
Return the skillet to the heat and add the onion. Saute for 4 minutes, then add the cinnamon, curry powder and smoked paprika. Saute for 30 seconds, then add the apples. Toss well to coat the apples with the seasonings, then cover the pan, reduce the heat to low and cook for 5 minutes, or until the apples are tender but not mushy.
Uncover the pan and stir in the vinegar. In a small glass, mix together the water and cornstarch, then add to the skillet. Stir and then bring to a simmer. Return the chicken to the skillet, cover with the sauce, then cover the skillet and cook for 6 to 8 minutes, or until the sauce has thickened and the chicken is fully cooked. Season with salt and pepper.
Serve the chicken with the apple sauce spooned over it.