Preheat the oven to 350º Fahrenheit. Spray a 9x13 baking pan with cooking spray.
Cream the butter and sugar together until smooth.
Add the eggs and vanilla. Beat well.
In a separate bowl, whisk together the flour, baking powder, soda and salt.
Add the flour mixture to the creamed butter alternately with the sour cream.
Fold in the chopped apple.
Spread the batter in the prepared pan.
In a small bowl, mix together the brown sugar, cinnamon, butter and nuts.
Sprinkle over the batter.
Bake for 35-40 minutes or until the cake tests done.
Store in an airtight container at room temperature.
The calories shown are based on the cake being cut into 15 pieces, with 1 serving being 1 slice of cake. Since different brands of ingredients have different nutritional information, the calories shown are just an estimate. **We are not dietitians and recommend you seek a nutritionist for exact nutritional information.**