Arrange apple slices in greased 2 quart round casserole.
Sprinkle cinnamon, lemon and orange rinds and both liqueurs on top of apples.
In a separate bowl, mix sugars, flour, salt and butter with a pastry blender or in a processor until crumbly; add the chopped walnuts..
Spread mixture over top of apples.
Bake uncovered at 350 degrees until apples are tender and top is lightly browned, approximately 1 hour.
Serve warm with cream, whipped cream or with vanilla or cinnamon ice cream.