In a medium bowl, combine the chopped pecans, light brown sugar, and ground cinnamon. Mix until evenly coated and set aside.

Preheat your oven to 350°F (175°C) and prepare a baking pan by greasing it lightly.

In a saucepan over medium heat, melt the unsalted butter until it turns a deep golden brown, then let it cool.

In a separate bowl, whisk together the all-purpose flour, baking powder, baking soda, and salt.

In a large mixing bowl, beat the cooled brown butter with granulated sugar until smooth. Add the egg and vanilla extract.

Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Fold in the sour cream.

Pour half of the batter into the prepared pan, sprinkle with half the pecan topping, then add the remaining batter.

Bake for 30-35 minutes until a toothpick comes out clean. The edges should be golden-brown.

Let the cake cool in the pan for 10-15 minutes before transferring to a wire rack to cool completely.