01 - Preheat oven to 350°F. Grease and flour a 9x13-inch baking pan.
02 - In a medium bowl, combine chopped pecans, brown sugar, flour, cinnamon, and melted butter. Stir until the mixture forms coarse, crumbly clusters. Set aside.
03 - In a bowl, whisk together flour, baking powder, baking soda, and salt until evenly distributed.
04 - In a large bowl, beat softened butter and granulated sugar with an electric mixer until pale, light, and fluffy.
05 - Add eggs one at a time to the butter mixture, beating well after each addition. Blend in sour cream and vanilla extract until smooth.
06 - Gradually fold the dry ingredient mixture into the wet ingredients, mixing until just combined. Do not overmix.
07 - Spread half the batter evenly across the bottom of the prepared pan. Sprinkle half the topping mixture over the batter. 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.