Makes 1 dozen cupcakes
Preheat the oven to 350° F. Place 10 paper liners into the cups of a muffin pan.
In a large mixing bowl with an electric mixer, beat together the oil, sugar, egg, vinegar, vanilla and food coloring until combined.
In a smaller bowl, stir together the flour and baking soda. Add to the egg mixture, in two or three additions alternately with the buttermilk, beating well after each.
Spoon the batter into the 10 paper liners, dividing the batter evenly among them.
Bake for 20 to 25 minutes or until a toothpick poked into the middle of a cupcake comes out clean. Remove from pan and let cool thoroughly.
Meanwhile, make the icing. In a medium bowl with an electric mixer, beat the butter until creamy. Add the icing sugar gradually, in 3 or 4 additions, beating very well after each addition. Beat in the vanilla. Add the milk or cream, one tablespoon at a time, beating well, until the icing is creamy and spreadable -- the more you beat this, the better it will be. Add food coloring, if using it, beating it in gradually until the icing is tinted the way you like it.
Decorate cupcakes with green sprinkles or coloured sugar, shamrocks made out of gummy candies -- or whatever else your little leprechaun can think of.