Preheat your oven to 350°F (175°C). Grease a baking dish.
In a mixing bowl, cream together the softened butter and granulated sugar until light and fluffy. Beat in the eggs, one at a time, then stir in the sour cream and vanilla extract.
In another bowl, whisk together the flour, baking powder, baking soda, and salt. Gradually add this to the wet mixture, mixing until just combined.
Fold in the apple pie filling and chopped walnuts if using.
Pour the batter into the prepared baking dish.
In a separate bowl, mix together the crumb topping ingredients until crumbly. Sprinkle over the batter.
Bake for 30 minutes or until a toothpick inserted comes out clean.
Notes
Let the cake cool before slicing. This cake is best served warm.
Keyword apple dessert, apple pie filling coffee cake, coffee cake