Preheat oven to 350F and line a 9x9 baking pan with parchment paper.

Melt the butter in a saucepan over medium heat.

Stir in the dark brown sugar, eggs, and vanilla extract until well combined and melted.

In a separate large bowl, whisk together the flour, baking powder, and salt.

Pour the wet mixture into the dry ingredients and stir with a wooden spoon until smooth.

Fold in the chopped pecans.

Pour batter into the prepared pan and bake for 30-35 minutes until a toothpick inserted comes out clean.

Cool in the pan before cutting into squares.

Optional: top with powdered sugar before serving.