Preheat oven to 180C. Line a 12-hole medium-size muffin tin with paper cases.
Mix finely ground Coffee Beans and Boiling Water in a small bowl, and set aside.
Beat softened Butter in a mixing bowl with a whisk until smooth. Add Sugar and beat until creamy.
Add Eggs, one at a time, beating well after each addition. Add Coffee mixture, Milk and Self-Raising Flour, and mix with a spatula or large metal spoon until just combined. DO NOT over-mix.
Spoon the mixture into paper cases. Bake for about 20 minutes or until golden and cooked through. Leave in tins for 5 minutes before moving onto wire rack to cool.
To make Coffee Butter Cream, place softened Unsalted Butter in a mixing bow, add all other ingredients except Milk, and mix well. If the cream is too thick, add a small amount of Milk, and mix well until smooth.
Spread the Coffee Butter Cream on the cooled cupcakes. You may prefer piping out the cream using a piping bag.
