Buttercream frosting, made from a mixture of butter, powdered sugar, vanilla and milk, is a classic frosting for decorating cakes, but it might prove too rich and sweet for your taste. Whipped frosting made from flour and granulated sugar has a light, airy texture similar to whipped cream with a more subtle flavor that won't overpower the flavors of the cake. Unlike using whipped cream as frosting, this whipped frosting has the rich buttery flavor you expect from frosting and it holds its shape without melting.
Whisk flour and milk together in a medium saucepan. A large cake or roughly 24 cupcakes need about 1 cup of milk and 1/4 cup of flour.
Heat the flour and milk together over medium to heat, stirring constantly, just until it begins to boil. Reduce the heat to low and cook the mixture until it thickens to a consistency similar to thick pancake batter. Stir the mixture constantly while cooking to get rid of all lumps and so nothing sticks to the bottom of the pan. Remove the pan from the heat and let it cool completely.
Beat softened, unsalted butter in a mixing bowl for several minutes until it becomes light and fluffy. Add granulated sugar to the butter and continue mixing on high speed for about five minutes until the sugar is completely dissolved in the butter and the mixture is smooth. For every 1 cup of milk used in the milk and flour mixture, you'll need 1 cup of butter and 1 cup of granulated sugar. You can substitute caster sugar for granulated sugar, which is finer than granulated sugar, but coarser than powdered sugar.
Reduce the electric mixer to low speed and add the cold flour and milk mixture to the sugar and butter mixture. Mix just until well combined.
Increase the speed to medium and beat the mixture for about five minutes or until the frosting becomes light and airy, much like the consistency of whipped cream. Add pure vanilla extract to the mixture to taste and mix just until thoroughly incorporated. How much vanilla you use is up to you, but you might try 1 to 1 1/2 tablespoons of vanilla for every 1 cup of sugar and butter in the recipe.