01 - Preheat the oven to 350°F (175°C). Grease and flour a 9x13-inch baking pan.
02 - In a medium bowl, combine the chopped pecans, packed light brown sugar, flour, ground cinnamon, and melted butter. Stir until the mixture resembles coarse crumbs. Set aside.
03 - In a bowl, whisk together the all-purpose flour, baking powder, baking soda, and salt until evenly distributed.
04 - In a large bowl, beat the softened butter and granulated sugar together using an electric mixer until pale, light, and fluffy.
05 - Add the eggs one at a time to the butter mixture, beating well after each addition. Mix in the sour cream and vanilla extract until smooth.
06 - Gradually fold the dry ingredient mixture into the wet ingredients, stirring gently until just combined. Do not overmix.
07 - Spread half of the batter evenly across the bottom of the prepared pan. Sprinkle half of the crunch topping over the batter layer. Spread the remaining batter on top and finish with the rest of the topping.
08 - Bake for 35 to 40 minutes, or until a toothpick inserted into the center comes out clean.
09 - Let the cake cool in the pan on a wire rack for at least 20 minutes before slicing and serving.