01 - Preheat oven to 350°F (175°C). Grease a 9x13-inch baking dish or a 9-inch round springform pan with butter or nonstick spray.
02 - In a medium bowl, combine the chopped pecans, packed light brown sugar, ground cinnamon, all-purpose flour, and melted unsalted butter. Stir until the mixture resembles coarse crumbs and set aside.
03 - In a separate bowl, whisk together the all-purpose flour, baking powder, baking soda, and salt until evenly distributed.
04 - In a large mixing bowl, beat the softened unsalted butter and granulated sugar using an electric mixer on medium speed until pale, light, and fluffy, about 3 minutes. Add the eggs one at a time, beating well after each addition, then blend in the vanilla extract.
05 - Add the dry ingredient mixture and sour cream to the butter mixture in alternating batches, beginning and ending with the flour. 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 over the batter in an even layer. Spread the remaining batter on top and finish with the rest of the crunch mixture.
07 - Bake for 40 to 45 minutes, or until the top is golden brown and a toothpick inserted into the center comes out clean.
08 - Allow the cake to cool in the pan for 20 minutes before slicing into squares and serving warm.