Place tea bags in a glass measuring cup; pour boiling water over tea bags. Let steep 8 minutes. Remove and discard tea bags; cool tea completely.
Combine flour, baking powder, salt, and cocoa, and set aside.
Beat butter at medium speed with an electric mixer 2 minutes or until creamy. Gradually add sugar, beating 5 to 7 minutes. Add eggs, 1 at a time, beating just until yellow disappears. Set aside.
Stir together milk and tea. Add the flour mixture to the butter mixture alternately with the milk mixture, beginning and ending with flour mixture. Mix at low speed after each addition, just until blended. Stir in vanilla.
Pour batter into a greased and floured 10-cup Bundt pan. Bake at 300° for 1 hour and 15 minutes or until a toothpick inserted in center comes out clean. Cool cake in pan on a wire rack 10 to 15 minutes; remove from pan, and cool cake completely on a wire rack. Dust cake with powdered sugar, and serve with Earl Grey Dark Chocolate Sauce. Garnish, if desired.