TOPPING:Mix first four ingredients until crumbly,set a side.
CREAM IN A LARGE BOWL: Brown sugar, margarine, egg.
MIX TOGETHER IN A MED> BOWL: flour, baking soda, salt.
Start with flour mixture- mix a little into creamed mixture- than add sour cream- add flour- add sour cream and end by adding the rest of the flour mixture. Stir in the apples- put the mixture into oiled 9x14 baking dish- add topping- bake next day, keep in refrigerator over night. Bake at 325 degrees for 35 to 40 min. serve warm or cold.