Preheat your oven to 180C/350F and line a cake tin with greaseproof paper.
Place the sugar, flour, baking powder and salt into a bowl.
Add the butter and beat on low until the mixture has a wet sand appearance and no butter portions remain that are larger than a pea (the smaller the better), approximately 2 minutes.
Pour the milk, buttermilk and vanilla extract into a small jug and stir together until smooth, pour into the dry ingredients and combine on low until no dry portions remain in the bowl.
Scrape down the sides of the bowl and add in one egg and beat on low until it is fully combined, approximately 40 seconds.
Repeat with the remaining egg and beat until combined.
Pour evenly into the cake tin and spread out evenly.
Place in the oven until golden, approximately 45 minutes or until a skewer comes out clean.
Remove and allow to cool in the tin for 5 minutes before turning upside down onto a cooling rack.
Set aside to cool completely.