Beat the soft butter and sugar, with a hand held electric beater, till pale and creamy.
Sieve together the flour, cornstarch, salt, baking powder and flour. Add this, the extract (if using), and the milk and beat into the creamed mixture, on lowest speed, till just combined.
Spoon the batter evenly between 12 cupcake/ muffin tins (for largish cupcakes) or 20 cupcake/ muffin tins (for smaller cupcakes) lined with paper cases.
Bake at 180C (350F) for about 20 minutes, till done. Completely cool the cupcakes on a rack.
When ready to ice the cupcakes, mix the icing sugar, lemon juice and food colouring in a bowl. Slowly add the milk (or water) a little at a time, and mix into a thick and smooth paste. The icing should be thick enough to spread without running down the sides. If the icing is a little runny, add a little icing sugar to adjust consistency.
Pour about 1/2 a teaspoon or so of the icing on top of esch cupcake and allow to spread. Decorate with the silver decorations. Allow the icing about 15 to 20 minutes to set.