5 large egg whites, 1 cup plus 2 tablespoon of castor sugar, a pinch of salt, 454 gm unsalted butter, 1 teaspoon vanilla extract. Gradually add the sugar, beating continuously for 3 minutes until fluffy. Add the vanilla and beat well. Add the cooled milk mixture and continue to beat on medium high for 5 mins, until very smooth. Cover and refrigerate for 15 mins.