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 stir to cook for a couple of minutes. Sprinkle the flour over the chicken and onion mixture. Stir to combine, then stir in the curry powder. Cook the mixture over medium heat for 1 minute, stirring constantly. Pour in the chicken broth. Stir to combine and cook for a minute to thicken. Add the half-and-half, sugar and some salt and pepper and cook for another 5 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!