My microwave is 800 watts. The majority of microwaves are around 1000 watts. This will affect the cooking time of your cake. The higher the wattage of the microwave the quicker the cake will cook!
You will need a glass or plastic container approx. 20 cm x 9 cm (8 x . Line the container you use with a circle (or square) of baking paper that fits exactly Into the bottom of the container and then spray with nonstick spray.
Sift the flour, cocoa and baking powder together and whisk in the sugar to combine everything. ( Or if you have no sifter put them into a bowl and whisk together)
Mix the water, egg and oil together and add to the dry ingredients. Mix with a whisk till smooth
*For an 800 watt microwave: Pour the mixture into the lined mold and microwave for 5 minutes. Open the door turn the container. The middle of the cake will look like a volcanic eruption. It will need a little longer. Reset the timer for 3 minutes. Insert a skewer into the centre of the cake. The very top may be sticky to the finger, but the centre skewer should come out pretty clean. It is most likely Once the 3 minutes is up, keep the door closed for at least a minute. 1000-1200 watt microwave. Set the oven to 2 minutes. check the cake and set at 2 minute intervals checking as above by using a skewer. Then leave in the oven with the door closed for another minute or so. Run a knife around the container, put a plate on top and turn the cake over so that it slips out of the mould
Either, eat the cake with cream or icecream and chocolate sauce, straight away. Find the chocolate sauce recipe. You can also cool and ice this cake if needed. Best the day it's made.