Heat oil in a skillet over medium heat and sauté the onion until caramelized.
Add the apple, garlic, and ginger, and cook for another 2 minutes.
Stir in the curry powder, turmeric, cumin, coriander, and cinnamon, and cook for 1 minute.
Sprinkle in the flour, mix well, and cook for 2 minutes.
Gradually add the chicken stock, stirring constantly to prevent lumps.
Add tomato puree, sugar, and Worcestershire sauce. Simmer for 15 minutes.
Blend the sauce for a smoother texture, if desired.