Preheat oven to 175 degrees celsius (fan-forced).
Grease and line a round 20cm cake tin with baking paper and set aside.
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 (approximately 5 minutes).
Slowly add the eggs (one at a time) while continuing to beat through until completely combined.
Sift in the self raising flour and stir with a spoon until just combined (don't over-mix).
Pour the mixture into the prepared tin and bake for 25-30 minutes or until tested with a skewer (see notes).
Leave the cake to cool in the tray for 15 minutes before moving to a wire rack to cool completely.
To make the icing, beat the butter in a bowl until pale and fluffy (approximately 5 minutes).
Slowly add the icing sugar mixture, milk, vanilla extract and food colouring and continue to beat until smooth and creamy.
Spread the buttercream frosting over the cooled cake and serve.
Keep any leftover cake in an airtight container at room temperature for up to 4 days.