Preheat your oven to 350°F (175°C) and prepare two 9-inch round cake pans by greasing them and lining the bottoms with parchment paper.

In a mixing bowl, cream together the softened unsalted butter and granulated sugar until light and fluffy, about 3-5 minutes.

Add the eggs one at a time, mixing thoroughly after each addition. Then mix in the vanilla extract.

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

Gradually add the dry ingredients to the wet mixture, alternating with buttermilk, mixing on low speed just until combined. Fold in the chopped pecans.

Divide the batter evenly between the prepared pans and smooth the tops before baking.

Bake for 25-30 minutes, or until a toothpick inserted in the center comes out clean.

Allow the cakes to cool in the pans for 10 minutes before transferring to wire racks to cool completely.

While the cakes cool, prepare the frosting by melting the butter with brown sugar and milk in a saucepan. Bring to a boil and let bubble for 2-3 minutes.

Remove from heat, cool slightly, then whisk in powdered sugar and vanilla until smooth.

Once the cakes are cool, frost the top of one layer, stack the second layer on top, and frost the top and sides of the cake.

Garnish with chopped toasted pecans if desired before serving.