Place the butter into your mug and melt for 30 seconds (or until melted).
Add the milk and vanilla extract and stir to combine.
Add the gluten free plain flour, gluten free baking powder, caster sugar and stir to combine. Add the sprinkles and stir.
Microwave for 1 minute. The cake should be cooked on the top while staying soft in the middle.If you think it's still a little undercooked (all microwaves are very different), cook for a further 10 - 20 seconds on medium, in 10 second bursts.
Serve while warm with ice cream (optional).
Notes
RECIPE NOTES & TIPS
Gluten free baking powder - check that your baking powder is gluten free (most are). I use McKenzie's brand which is gluten free.
Cooking time - all microwaves vary greatly with how long they will take to cook this mug cake. I recommend cooking it for 1 minute to start, and then in 10 second extra bursts if needed.
Don't overcook the mug cake! - Stop cooking when the cake is set on top.
If you think it's still a little undercooked (all microwaves are very different) - cook for a further 10 - 20 seconds on medium, in 10 second bursts.
Watch the cake - watch it carefully in the microwave to make sure it doesn't overflow.
Make 2 portions - you can make this mug cake in two smaller mugs or ramekins rather than 1 large mug/ramekin.