Preheat the oven to 190 degrees C. Line a 12 hole cupcake tray with patty cups.
Beat together the butter and sugar in a bowl until light and fluffy. Beat in a separate bowl the eggs. Add a little of the eggs to the butter mixture and beat. Add flour and milk slowly and beat the mixture until smooth.
Divide the mixture between the patty cups and bake in the oven for 12 - 15 minutes until golden brown and firm to the touch.
Remove the cakes from the oven and transfer to a cake rack to cool.
To prepare buttercream: Beat the butter or margarine in a bowl to soften it. Add the icing sugar, boiling water and vanilla. Beat until the icing is very smooth.
Ice each cooled cake using a piping bag. Decorate with cake decorations of choice.