Preheat the oven to 350º Fahrenheit. Spray a 9×13 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.
Spread the batter in the prepared pan.
Sprinkle the chopped apples on top of the batter
In a small bowl, mix together the oats, flour, brown sugar, baking powder & soda, cinnamon and melted butter.
Sprinkle the topping over the batter.
Bake for 40-45 minutes or until the cake tests done.
In a small bowl, mix together the powdered sugar, apple cider and 2 tablespoons heavy cream. Whisk together to combine well. Add another tablespoon or two of heavy cream if needed until the glaze is at drizzling consistency.