Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round cake pans, then line the bottoms with parchment paper.
In a large mixing bowl, cream together the softened butter and granulated sugar until light and fluffy using an electric mixer or stand mixer.
Beat in the eggs, one at a time, mixing well after each addition. Stir in the vanilla extract.
In a separate bowl, combine the buttermilk and vanilla extract.
In another bowl, sift together the all-purpose flour, baking powder, baking soda, and salt.
Gradually add the dry ingredients to the creamed mixture alternately with the buttermilk mixture, beginning and ending with the dry ingredients. Mix until just combined.
Fold in the chopped pecans until evenly distributed throughout the batter.
Divide the batter evenly between the prepared cake pans and smooth the tops with a spatula.
Bake in the preheated oven for 25-30 minutes, or until a toothpick inserted into the center comes out clean.
Remove the cakes from the oven and let them cool in the pans for 10 minutes before transferring them to a wire cooling rack to cool completely.
While the cakes are cooling, prepare the frosting. In a saucepan, melt the butter over medium heat. Stir in the packed brown sugar and milk, and bring the mixture to a boil. Boil for 2 minutes, stirring constantly.
Remove the saucepan from the heat and let the mixture cool slightly.
Gradually beat in the powdered sugar and vanilla extract until smooth.
Stir in the chopped pecans until evenly distributed throughout the frosting.
Once the cakes are completely cooled, frost the top of one cake layer with the pecan frosting. Place the second cake layer on top and frost the top and sides with the remaining frosting.
Slice and serve the Butter Pecan Cake, and enjoy the rich, nutty flavors with every bite!