Callistemon, you can probably use the cocoa - but make up your own mind (and don't blame me)!
www.canitgobad.net/can-cocoa-powder-go-bad/
nanasam, you're supposed to cook it in a large mug, but I use a small glass pudding basin:
4 tbsp plain flour
2 tbsp sugar
2 tbsp cocoa
1 egg
3 tbsp milk
3 tbsp oil (I use rapeseed - or vegetable, usually is rapeseed, but cheaper - such is marketing)
(dash of vanilla if you have it)
Mix the dry ingredients
beat the egg (with a pinch of salt if you like)
add the milk and oil then mix
stir all ingredients together
Microwave about 3 mins for 800 watts (mine is 1000 watts so 2 for me - depends on your mug/bowl shape too).
It makes a rather chewy cake (nice enough with raspberry jam) or a quite acceptable chocolate pudding. In this house, chocolate sauce is just custard with cocoa mixed in the powder. Try it!
(Then I feel suitably guilty as a failed vegan/veggie, but it doesn't seem that important at the moment.)