Measure the self-rasing flour and the caster sugar into a large mug, mix to combine.
Melt the butter, once melted. Stir the white chocolate chips into the melted butter
Add the white chocolate and melted butter to the mug of dry ingredients along with all the remaining ingredients (milk, vanilla extract)
Mix well to combine the ingredients into a vanilla cake batter.
(Optional) Pour half of the batter into a second mug (you can make it all in one mug but it will need to be very large.
Microwave on high power for 90 seconds until the mug cakes are cooked and risen.
Add sprinkles if desired
Notes
Be sure to mix the batter well, if it's not mixed well you can find lumps of flour right at the bottom of your mug cake.
To elevate these cakes even further for special occasions try topping with whipped cream, vanilla ice cream, sprinkles or fresh berries.
Mug cakes are best enjoyed straight away while they are still warm.
Self-raising flour: This can be substituted for plain all purpose flour and ¼ teaspoon of baking powder. I have also tested this recipe with self-raising gluten-free flour and it worked just fine.
Caster sugar: I like to use finer sugar like caster sugar, but regular granulated sugar will be just fine.
Milk: This can be substituted for a plant-based milk
Butter: This can be substituted for margarine
Vanilla: I like to use a pure vanilla extract rather than an artificial vanilla essence as the vanilla flavor is just so much nicer.