In a microwaveable mug, mix together the egg, oil, milk and vanilla
Add in the Flour, sugar, baking powder and salt and mo until combined. Use a fork to whisk and get out any lumps.
Melt the butter and sugar together for the top of the cake.
Once melted mix in the pineapple and lay nicely on top of your cake.
Stay might sink a little as it is a thin cake
Microwave for 1 minute, then check and possible cook for another 20 seconds. This cake takes a little longer to cook (timing is based on my 1200W microwave so your timing might vary)