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 the mixture becomes 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 using an electric mixer until light and fluffy, approximately 3 minutes.
05 - Add the eggs one at a time, beating well after each addition. Mix in the vanilla extract until fully incorporated.
06 - Alternately add the dry flour mixture and the sour cream to the butter mixture, beginning and ending with the flour mixture. Fold gently until just combined, being careful not to overmix.
07 - Spread half of the cake batter evenly into the prepared pan. Sprinkle half of the cinnamon pecan crunch mixture uniformly over the batter.
08 - Carefully spread the remaining batter over the pecan layer, smoothing the top. Finish by sprinkling the remaining pecan crunch mixture evenly across the surface.
09 - Bake for 40 to 45 minutes, or until a toothpick inserted into the center of the cake comes out clean. The top should be golden brown and fragrant.
10 - Allow the cake to cool in the pan for 20 minutes before slicing. Serve warm or at room temperature.