Melt chocolate and butter over very low hear, stirring constantly. Cool slightly, set aside 1/3 cup. Combine sugar, salt, milk and vanilla, blend.
Add remaining chocolate mixture, mix well. Let stand stirring occasionally, until of right consistency to spread. (If necessary, add additional milk a teaspon at a time)
Fill and frost top and sides of three 8-inch or two 9-inch layers.
Pour reserved mixture over top and allow to drizzle down sides.