01 - Preheat oven to 350°F. Grease and flour a 9x13-inch baking pan.
02 - In a medium bowl, combine the chopped pecans, brown sugar, flour, cinnamon, and melted butter. Mix until the mixture becomes crumbly and well combined. Set aside.
03 - In a bowl, whisk together the 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 the mixture is light and fluffy, approximately 3 minutes.
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 ingredients into the wet mixture, stirring gently until just combined. Avoid overmixing to keep the cake tender.
07 - Spread half of the batter evenly across the bottom of the prepared pan. Sprinkle half of the crunch topping over the batter layer. Repeat with the remaining batter, spreading it evenly, and top with the rest of the crunch topping.
08 - Bake for 35 to 40 minutes, or until a toothpick inserted into the center of the cake comes out clean. The top should be golden brown and slightly firm to the touch.
09 - Allow the cake to cool in the pan on a wire rack for at least 20 minutes before slicing into squares and serving.