Preheat your oven to 350°F (175°C) and prepare two 9-inch round cake pans by greasing them with unsalted butter and dusting with flour.

In a large mixing bowl, cream together 1 cup of softened unsalted butter and 2 cups of granulated sugar until light and fluffy, about 3-5 minutes.

Add 4 large eggs one at a time, mixing well after each addition, then stir in 1 tablespoon of vanilla extract.

In another bowl, whisk together 3 cups of all-purpose flour, 1 teaspoon of baking powder, 1 teaspoon of baking soda, and 1 teaspoon of salt.

Gradually add the dry mixture to the wet batter in three parts, alternating with 1 cup of buttermilk, mixing until just combined, then fold in 1 cup of toasted, chopped pecans.

Divide the batter evenly between the prepared pans and bake for 25-30 minutes, or until golden brown and a toothpick comes out clean.

Allow the cakes to cool in the pans for about 10 minutes, then turn them out onto wire racks to cool completely.

For the frosting, melt ½ cup of unsalted butter with 1 cup of brown sugar and ¼ cup of milk in a saucepan over medium heat, bring to a boil while stirring, then remove from heat and cool slightly. Mix in 2 cups of powdered sugar and 1 teaspoon of vanilla extract until smooth.

Once the cakes are cool, frost the top of one layer with brown sugar frosting, place the second layer on top, then frost the top and sides of the cake, garnishing with extra toasted pecans if desired.