Preheat oven to 350 degrees.
Lightly grease a 8x8 or 9x9 baking dish and set aside.
In a medium bowl measure out 2/3 cup yellow cake mix, Add melted butter, brown sugar, and nuts. Mix well. Set aside.
In a large bowl combine rest of dry cake mix from box, eggs, and sour cream. Mix for about 3 minutes until batter is smooth and fluffy.
Pour half the cake batter into prepared baking dish and smooth out. Top with 1/2 of the crumble mixture evenly. Repeat with rest of cake batter and then top with rest of crumble.
Bake for 45 minutes to an hour until toothpick comes out clean. Cool for a few minutes and enjoy.
