Preheat oven to 180c and lightly grease muffin pan.
Mix self raising flour, caster sugar, cocoa powder and baking powder in large mixing bowl until combined.
In a separate bowl; mix vegetable oil, buttermilk, egg, vanilla extract and salt until combined.
Make a well in the dry ingredients bowl, pour in the wet ingredients and mix until JUST combined and no streaks of flour remain. Do not over mix, the mixture should be lumpy. This helps keep the muffins moist.
Evenly distribute the mixture into the prepared muffin pan.
Place a mini creme egg in the centre of each muffin, stood up straight.
Bake for 15 minutes or until the muffin springs back when lightly pressed.
FOR THE FROSTING
In a bowl, cream together cream cheese and butter until creamy.
Mix in the vanilla extract, then gradually stir in the icing sugar.
Transfer mixture into piping bag and pipe onto muffins.