01 - Preheat oven to 350°F (175°C). Grease a 9x13-inch (23x33 cm) baking dish or a 9-inch (23 cm) 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 butter and granulated sugar using an electric mixer until light and fluffy. 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 creamed butter mixture, starting and ending with the flour mixture. Fold gently until just combined, being careful not to overmix.
06 - Spread half of the cake batter evenly into the prepared pan. Sprinkle half of the cinnamon pecan crunch mixture uniformly over the batter.
07 - Spread the remaining batter over the filling layer, then top with the remaining cinnamon pecan crunch mixture, pressing gently to adhere.
08 - Bake for 40 to 45 minutes, or until a toothpick inserted into the center of the cake comes out clean.
09 - Allow the cake to cool in the pan for 20 minutes before slicing and serving.