01 - Preheat oven to 350°F. Grease a 9x13-inch baking dish or a 9-inch round springform pan with butter or non-stick spray.
02 - In a medium bowl, combine the chopped pecans, brown sugar, cinnamon, flour, and melted butter. Stir until the mixture forms coarse, crumbly clumps. Set aside.
03 - In a separate medium bowl, whisk together the flour, baking powder, baking soda, and salt until evenly distributed.
04 - In a large mixing bowl, beat the softened butter and granulated sugar with an electric mixer on medium speed until pale, 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 flour mixture and the sour cream to the butter mixture in three additions, beginning and ending with the flour. Fold gently until just combined — avoid overmixing to keep the crumb tender.
06 - Spread half of the batter evenly into the prepared pan. Sprinkle half of the cinnamon pecan crunch mixture over the batter in an even layer. Spread the remaining batter on top and finish with the rest of the pecan crunch topping.
07 - Bake for 40 to 45 minutes, or until the top is golden brown and a toothpick inserted into the center comes out clean.
08 - Allow the cake to cool in the pan for 20 minutes before slicing. Serve warm or at room temperature.