Combine flour, baking powder and salt; set aside. Beat egg whites with an electric mixer at high speed until foamy. Gradually add 1/4 cup sugar, 1 tablespoon at a time, beating until stiff peaks form and sugar dissolves, about 2 to 4 minutes; set aside.
Beat egg yolks in a large mixing bowl with an electrix mixer at high speed, gradually adding 1/2 cup sugar; beat 5 minutes, or until thick and pale. Add water and vanilla extract; beat well. Add flour mixture; beat just until blended. Fold in about 1/3 of egg white mixture. Gently fold in remaining egg white mixture.
Grease bottom and sides of a 15"x10" jelly-roll pan. Line with wax paper; grease and flour. Spread batter evenly into pan. Bake at 375° for 10 minutes, or until springs back when lightly touched. Sift powdered sugar in a 15"x10" rectangle on a cloth. When cake is done, immediately loosen from sides of pan; turn out onto cloth. Peel off wax paper. Starting at narrow end, roll up cake and cloth together; cool completely on a wire rack, seam side down.
Unroll cake and remove towel. Spread half Chocolate Frosting onto cake; carefully reroll. Cut a 1-inch-thick diagonal slice from one end of cake roll. Place cake roll on a serving plate, seam side down. Position slice against side of cake roll to assemble knot; use frosting to "glue" in place. Spread remaining frosting over cake and knot. If frosting is soft, chill cake before serving. Garnish with fresh mint and fresh cranberries.
Chocolate Frosting: In a large bowl, combine powdered sugar and cocoa. Add milk and butter to sugar mixture; beat with an electric mixer at medium speed until smooth.