Preheat oven to 175 degrees celsius (fan-forced). Place cupcake cases into the holes of two 12-hole muffin trays.
Place the butter, caster sugar, salt and vanilla extract into a bowl.
Beat together with a stand-mixer or hand-held beaters until pale and fluffy.
Add the eggs one at a time and beat through.
Sift in the self-raising flour, add the chocolate chips, and stir with a spoon until just combined (don't over mix).
Place the cupcake mixture into the cupcake cases - filling them to ⅔ full.
Bake in the oven for 12-15 minutes or until golden and they spring back when touched in the centre (if you're making mini cupcakes, reduce the cooking time slightly).
Leave cupcakes in the baking trays for 5 minutes before moving to a wire rack to cool completely.
To make the buttercream frosting, beat the butter in a bowl until pale and fluffy (approximately 5 minutes).
Slowly add the icing sugar mixture, milk and vanilla extract and continue to beat until smooth and creamy.
Spread buttercream frosting over cupcakes when they have completely cooled and sprinkle with extra chocolate chips.