Melted butter, to grease
450g (3 cups) self-raising flour
150g (1 cup) plain flour
440g (2 cups) caster sugar
300g butter, cubed, at room temperature
310ml (1 1/4 cups) milk
6 eggs, at room temperature
3 tsp vanilla essence

Method
Preheat oven to 140°C. Position a rack on the second lowest shelf of the oven. Brush a round 25cm (base measurement) cake pan with the melted butter to lightly grease. Line base and sides with non-stick baking paper.
Place the self-raising flour, plain flour, sugar, butter, milk, eggs and vanilla essence in a large mixing bowl. Use an electric beater to beat on low speed for 30 seconds or until just combined. Increase the speed to high and beat for 1-2 minutes or until the mixture is thick and all the butter is incorporated. Spoon the mixture into the prepared pan and smooth the surface with the back of a spoon.
Bake in preheated oven for 2 1/2 hours or until a skewer inserted into the centre of the cake comes out clean. Remove from oven and set aside for 10 minutes. Turn onto a wire rack for 2 hours or until completely cool.
Notes
Have the butter at room temperature, soft enough to beat, but not melted. The undecorated cakes will keep in an airtight container for up to 3 days.

Variations
Rich chocolate cake: Reduce the self-raising flour to 300g (2 cups). Sift 95g (1 cup) cocoa powder and 1/2 tsp bicarbonate soda, and add with the flours. Increase the milk to 435ml (1 3/4 cups). Omit the vanilla essence.
Orange cake: Reduce the milk to 185ml (3/4 cup) and add with 2 tbs finely grated orange rind and 125ml (1/2 cup) orange juice. Omit vanilla essence.
Carrot cake: Add 1 tsp ground cinnamon with the flours. Reduce the vanilla essence to 1 tsp. Add 285g (3 cups) coarsely grated carrot and 100g roughly chopped walnuts.
Banana cake: Sift 1 tsp bicarbonate soda and add with the flours. Reduce the milk to 125ml (1/2 cup). Add 390g (1 1/2 cups) mashed very ripe banana with the milk. Reduce the vanilla essence to 1 tsp