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 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 mix 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 mixture. Fold 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 pecan layer, then top with the rest of the crunch mixture, pressing gently to adhere.
08 - Bake for 40 to 45 minutes, or until a toothpick inserted into the center 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. Serve warm for the best texture.