Coat 3 (8-inch) round cake pans with cooking spray, and dust with 1 tablespoon flour.
Combine cocoa and chocolate in a small bowl; add boiling water, stirring until chocolate melts. Set aside.
Combine sugars, butter, and oil in a large bowl, and beat at medium speed of a mixer until well-blended (about 5 minutes). Add yogurt, extracts, and egg whites; beat well.
Lightly spoon sifted flour into dry measuring cups, and level with a knife. Combine sifted flour, baking powder, baking soda, and salt. Add flour mixture to creamed mixture alternately with buttermilk, beginning and ending with flour mixture. Beat in cocoa mixture.
Pour cake batter into prepared pans. Sharply tap pans once on counter to remove air bubbles. Bake at 350° for 25 minutes or until a wooden pick inserted in center comes out clean. Cool in pans 10 minutes, and remove from pans. Cool completely on wire racks.
Place 1 cake layer on a plate; spread with 1/3 cup Coconut-Pecan Frosting, and top with another cake layer. Spread with 1/3 cup frosting, and top with remaining cake layer. Spread remaining frosting over top and sides of cake. Store cake loosely covered in refrigerator.