Wash, blanch and dry the Kangaroo tail thoroughly. Divide it at the joints. Fry the tail lightly in hot butter, remove from pan.
In the same pan add the sliced onions and fry for a few minutes without browning. Sprinkle in the flour and curry powder, stirring until all the flour is incorporated. Add the stock and diced apple and return the tail to the pan. Cover closely and cook gently until tender, about 2 1/2 hours.
Add the lemon juice, taste and add salt if necessary. Arrange the pieces of tail on a hot dish, strain the sauce over and serve with boiled rice.