Heat oven to 350 degrees F. Coat two 9-inch round cake pans with nonstick spray.
In a medium bowl, whisk together flour, cocoa powder, baking soda and salt. In a large bowl, beat butter with an electric mixer on medium speed until smooth. Add brown sugar; beat until combined. Beat in eggs, one at a time, and vanilla. With the electric mixer on low speed, alternately beat in flour mixture and buttermilk, beginning and ending with flour. Spread cake batter evenly into prepared pans.
Bake at 350 degrees F for 30 minutes or until toothpick inserted in centers comes out clean. Cool in pans on wire rack for 10 minutes. Invert cakes directly onto racks; cool completely. While the cakes cool, make the frosting.
Place one cake layer on pedestal. Spread top with 1 cup frosting and 1/2 cup coconut. Add second layer. Spread frosting on top and side of cake. Press remaining 2-1/2 cups coconut into frosting. Garnish with raspberries and mint, if desired.
Place confectioners' sugar in a large bowl. Beat in boiling water. Add butter and cream cheese, beating well on medium-high speed after adding each piece. Beat in extract. Refrigerate until firmer consistency, 30 minutes to 1 hour.