01 - Preheat oven to 350°F. Grease a 9×13-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 resembles coarse crumbs and set aside.
03 - In a separate 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 together until light and fluffy. Add the eggs one at a time, beating well after each addition, then 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, 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 and top with the rest of the pecan crunch mixture, pressing gently to adhere.
08 - Bake for 40–45 minutes, or until a toothpick inserted into the center of the cake comes out clean and the top is golden brown.
09 - Allow the cake to cool in the pan for 20 minutes before slicing and serving.