Preheat your oven to 350°F (175°C).
Grease and flour three 9-inch round cake pans.
In a large bowl, combine the flour, sugar, cocoa powder, baking soda, baking powder, and salt.
In another large bowl, whisk together the buttermilk, vegetable oil, eggs, and vanilla extract until well combined.
Gradually add the wet mixture to the dry ingredients, blending until smooth.
Divide the batter evenly among the prepared pans and smooth the tops.
Bake for 30 to 35 minutes, or until a toothpick inserted in the center comes out clean.
Allow the cakes to cool in the pans for 10 minutes, then turn them out onto wire racks to cool completely.
Prepare the coconut-pecan frosting by combining the coconut, pecans, and sweetened condensed milk in a large bowl.
Once the cakes are completely cool, place one layer on a serving plate and spread a layer of frosting on top.
Repeat with the second layer, then place the third layer on top and frost the top and sides of the cake.
Let the cake set for at least 30 minutes before slicing and serving.
