Preheat the oven to 325 degrees. Prepare a 10” tube cake pan by greasing the sides and tube and lining the bottom with paper. Heat the chocolate in a double boiler over hot water until partially melted. Remove from the heat and stir rapidly until entirely melted; cool.
Measure the sifted flour, baking powder and salt; sift together. Cream the butter; gradually add the sugar, creaming after each addition until the mixture is very light and fluffy. This takes about 10 minutes with an electric mixer. Add the eggs, one at a time, beating well after each addition. Stir in the cooled chocolate and the vanilla. Beat well.
Alternately, add the flour mixture and the milk, beating well after each addition. Pour into the prepared 10” tube pan and bake for 1 hour and 30 to 35 minutes. Cool the cake in the pan for 15 minutes; then loosen from the tube and sides and remove from the pan. Cool completely. Drizzle with sweet chocolate glaze, if desired. To store this cake, wrap tightly and refrigerate.
Source: "Baker's Chocolate and Coconut Favorites", General Foods Kitchens, 1962