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, packed light brown sugar, ground cinnamon, all-purpose flour, and melted butter. Mix until the mixture becomes crumbly and well distributed. Set aside.
03 - In a separate bowl, whisk together the all-purpose flour, baking powder, baking soda, and salt until evenly blended.
04 - In a large mixing bowl, beat the softened unsalted butter and granulated sugar together using an electric mixer until the mixture is light and fluffy.
05 - Add the eggs one at a time to the butter mixture, 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. Mix 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 - Spread the remaining cake batter over the first pecan layer, then finish by sprinkling the rest of the cinnamon pecan crunch mixture on top.
09 - Bake for 40 to 45 minutes, or until a toothpick inserted into the center comes out clean.
10 - Allow the cake to cool for 20 minutes before slicing and serving.