In a separate large mixing bowl, beat together the butter and sugar on medium speed until light and creamy (about 3-5 minutes). Add the eggs, one at a time, beating well after each addition. Add the vanilla and beat to combine.
Add the butter and stir until melted. Heat to just below a boil and pour over the chocolate. Cover and let sit for about 5 minutes. Stir until all the chocolate is melted and the mixture is smooth and satiny. Pour over the cooled bars and spread evenly.