01 - Preheat oven to 350°F. Grease a 9x13-inch baking dish or a 9-inch round springform pan.
02 - In a medium bowl, combine the chopped pecans, brown sugar, cinnamon, flour, and melted butter. Mix until crumbly and well distributed. Set aside.
03 - In a separate bowl, whisk together the flour, baking powder, baking soda, and salt until evenly blended.
04 - In a large mixing bowl, beat the softened butter and granulated sugar together until light and fluffy, about 3 minutes. Add the eggs one at a time, beating well after each addition. Stir in the vanilla extract.
05 - Alternately add the dry ingredient mixture and the sour cream to the butter mixture, beginning and ending with the flour. Mix until just combined and avoid overmixing.
06 - Spread half of the cake batter evenly into the prepared pan. Sprinkle half of the cinnamon pecan crunch mixture over the batter in an even layer. Carefully spread the remaining batter on top, then finish with the rest of the pecan crunch mixture.
07 - Bake for 40 to 45 minutes, or until a toothpick inserted into the center comes out clean.
08 - Allow the cake to cool for 20 minutes before slicing and serving. Serve warm for the best texture.