Add the butter to a pot over medium heat and let it melt. Add the chicken and cook, stirring occasionally, until golden. Add the garlic and onions and cook, stirring, for a couple of minutes. Sprinkle the flour over the chicken and onion mixture and stir to combine. Stir in the curry powder and cook for 1 minute, stirring constantly. Pour in the chicken broth and stir to combine; cook for another minute to thicken. Add the half-and-half, brown sugar and some salt and pepper and cook for 5 more minutes.
Meanwhile, peel and dice the apple. Add the apples to the pot and cook for another 5 minutes. Taste, adjust the seasonings and serve!