Preheat oven to 325°.

To prepare streusel, lightly spoon ¼ cup flour into a dry measuring cup; level with a knife. Combine ¼ cup flour and brown sugar in a small bowl; cut in 2 tablespoons butter with a pastry blender or 2 knives until mixture resembles coarse meal. Stir in coconut and pecans. Set aside.

To prepare cake, coat a 12-cup Bundt pan with cooking spray; sprinkle with 1 tablespoon granulated sugar. Set aside.

Combine cocoa and baking chocolate in a small bowl; add boiling water, stirring until chocolate melts. Set aside.

Combine 1 ½ cups granulated sugar and ⅓ cup butter at medium speed of a mixer until well-blended (about 5 minutes).

Add vanilla and egg whites, 1 at a time, beating well after each addition.

Lightly spoon 2 cups flour into dry measuring cups; level with a knife. Combine the flour, baking powder, baking soda, and salt, stirring well with a whisk.

Add flour mixture to sugar mixture alternately with buttermilk, beginning and ending with flour mixture.

Stir in cocoa mixture. Spoon half of the batter into prepared pan; top with streusel.

Spoon remaining batter over streusel.

Bake at 325° for 1 hour or until a wooden pick inserted in center comes out clean.

Cool in pan on a wire rack 10 minutes; remove from pan. Cool completely.

To prepare glaze; combine powdered sugar and butter in a small bowl. Add milk; stir with a whisk. Drizzle over cake.