Preheat the oven to 350°F (175°C) and prepare two 9-inch round cake pans by greasing them with butter and dusting with flour.
In a large bowl, whisk together the flour, baking soda, baking powder, cocoa powder, sugar, and brown sugar until well combined.
In a separate bowl, mix the buttermilk, vegetable oil, eggs, and vanilla extract until smooth.
Gradually add the wet ingredients to the dry ingredients, stirring until fully combined.
Divide the batter evenly between the prepared pans and smooth the tops.
Bake in the preheated oven for 25-30 minutes, or until a toothpick inserted into the center comes out clean.
While the cakes cool, prepare the frosting by combining the sugar, evaporated milk, and butter in a saucepan over medium heat. Stir until the mixture comes to a boil.
Remove from heat and add vanilla extract, coconut, and pecans, mixing well.
Once the cakes are completely cool, layer them with the frosting between the cakes and on top.