Preheat over 325 degrees spray a 9x9 baking dish with cooking spray
Using a food processor combine the topping ingredients just until slightly clumpy set aside
Using a mixer cream butter and sugars together, add eggs one at a time then milk, sour cream and vanilla
In a separate bowl mix the flour. baking powder and salt then add it to the wet ingredients. mix until just combined.
Pour half of the cake batter into the prepared baking pan. Gently spread half the crumb mixture over the cake layer pressing gently. Carefully spread the remaining cake batter over the crumb mixture followed by the rest of the crumb mixture.
Bake for 1 hour until toothpick inserted in center comes out clean
Sprinkle powdered sugar (confectioners sugar) on top if desired