Preheat oven 350 deg. Butter and flour 2 round 23 cm cake pans. Melt chocolate and 0.5c water in top of double boiler. Let cool. Cream butter, sugar, and brown sugar together until light and fluffy, about 5 mins. Add vanilla and eggs, one at a time. Beat well after each addition. Beat in chocolate and mix well. Sift together flour, soda, and salt. Add flour to batter, alternating with milk, stir by hand just until batter is completely blended. Bake cakes 30-35 mins or until tester inserted comes out clean. Let cool on racks. Turn out the layers and allow to cool while you prepare frosting. Frosting: Melt chocolate over hot water, allow to cool. Place egg whites, sugar, cream of tartar, cold water, and salt in top of double boiler. Beat with electric mixer, 1 min. Place pan over steaming water (but not boiling) and continue beating for around 7 mins or until mixture is very thick and fluffy. Off the heat, fold in by hand the vanilla and melted chocolates. Place one cake layer on your serving dish and coat with frosting. Place on second layer and top with more frosting. Coat sides of cake as well. ----