Preheat oven to 350°F (175°C). Grease and flour three 9-inch round cake pans.

In a large bowl, beat together the butter and sugar until light and fluffy. Add eggs one at a time, beating well after each. Stir in the vanilla extract.

In a separate bowl, combine flour, baking powder, baking soda, and salt. Gradually add the dry ingredients to the wet mixture, alternating with milk, beginning and ending with flour. Fold in chopped pecans.

Divide the batter evenly between prepared pans. Bake for 25–30 minutes or until a toothpick inserted in the center comes out clean. Cool in pans for 10 minutes, then transfer to wire racks to cool completely.

To make the frosting, melt butter in a saucepan over medium heat. Stir in brown sugar and milk. Bring to a boil, remove from heat, and cool for 10 minutes.

Gradually beat in powdered sugar and vanilla extract until smooth.

Once cakes are completely cool, frost between the layers and over the top and sides of the cake. Garnish with whole pecans if desired.