Melt chocolate in top of double boiler. Stir flour into chocolate. Add milk a little at a time and blend well. Cook over medium heat, stirring constant ly, until very thick. Cool completely. In a large bowl, beat sugar, butter and vanilla until light and fluffy. Gradually add cooled chocolate mixture and beat until icing is the consist- ancy of whipped cream. This will frost tops and sides of 2-9" layers.
