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

In a medium skillet over medium heat, melt 4 tablespoons of unsalted butter, add 1 cup of chopped pecans and 1/2 cup of light brown sugar. Cook for 3-4 minutes until fragrant and golden.

In a separate bowl, combine 1 cup of buttermilk and 1/2 cup of milk. Mix well and set aside.

Whisk together 2 1/2 cups of all-purpose flour, 1 teaspoon of baking powder, 1 teaspoon of baking soda, and 1 teaspoon of salt in another bowl.

In a large mixing bowl, beat together 1 cup of softened unsalted butter and 1 1/2 cups of granulated sugar until light and fluffy. Add 1 tablespoon of vanilla extract.

Incorporate 4 large eggs one at a time, beating well after each addition.

Gradually add the flour mixture and milk mixture alternately to the butter mixture until just combined.

Gently fold in the toasted pecans.

Pour the batter into the prepared cake pans and bake for 25-28 minutes until a toothpick comes out clean.

Let the cakes cool in the pans for 15 minutes before inverting onto wire racks to cool completely.

Beat together 8 ounces of cream cheese and 1/2 cup of softened unsalted butter until smooth. Gradually add 4 cups of powdered sugar and 1 tablespoon of vanilla extract.

Assemble the cake by layering and frosting each layer with cream cheese frosting, garnishing with toasted pecans.