In a large saucepan, heat the oil until bubbling.
Saute the onion, garlic and curry powder in the heated oil, and season with salt & pepper to taste. Continue cooking until the onion turns a little translucent.
Mix in carrot, celery, chilis, and apple. Taste and test if you need to add any more salt and pepper.
Cook on medium-low heat for about 5 minutes, stirring consistently, until the vegetables soften.
Sprinkle the flour over the freshly-cooked mixture, and stir well until the flour is worked in and no white is shown.
Stir in the broth, a few ounces at a time, then add tomatoes and all tomato liquid (do not discard).
Add parsley, lemon juice, cloves, sugar, and bring to a boil.
Once it reaches a boil, bring down to simmer and add the chicken.
Stir every 15-20 minutes, and allow cooking between 90 minutes and four hours. The lower the temperature will require a longer cooking time.
Serve with warm naan bread.