In a medium mixing bowl combine sugar and flour; add the egg yolks. Beat mixture with a wire whisk until combined; set aside. In a heavy medium saucepan heat milk over medium heat just to boiling. Remove from heat. Gradually beat hot milk into egg mixture with the wire whisk; return entire mixture to saucepan. Cook over medium heat until bubbly, whisky constantly. Cook for 2 minutes more. Remove from heat. Add white baking bar, vanilla, and almond extract. Let stand 1 minute; stir until smooth.
Transfer mixture to a bowl. Cover surface with plastic wrap to prevent skin from forming; cool to room temperature. In a medium mixing bowl beat butter on medium to high speed until fluffy. Add cooled baking bar mixture, one-fourth at a time, beating on low speed after each addition until combined. Makes enough to frost tops and sides of two 8- or 9-inch layers.