Preheat your oven to 350°F (175°C) and prepare your cake pan by lining the bottom with parchment paper and greasing the sides.

In a large mixing bowl, cream the softened butter and sugar together using an electric mixer until light and fluffy, about 3 to 5 minutes.

Add the eggs one at a time, mixing well after each addition.

In a separate bowl, sift together the all-purpose flour and baking powder. Gradually add this to the butter-sugar-egg mixture, alternating with the buttermilk.

Fold in the toasted pecans gently into the batter.

Pour the batter into the prepared cake pan and bake for 30 to 35 minutes, until a toothpick inserted in the center comes out clean.

For the optional topping, combine brown sugar and butter in a saucepan over medium heat and stir until melted and bubbly.

Allow the cake to cool in the pan for about 10 minutes before transferring it to a wire rack.