Chocolate Cake in Slow Cooker

I was intrigued about the possibility of making a cake in a slow cooker - I've only ever done casserole-type dishes in it but my mother-in-law had in the past successfully made a lemon cake in one. So I got inspiration from various internet sources and managed to make this great little chocolate cake:

Ingredients:
2 eggs and the following ingredients each weighing the same amount as the 2 eggs together (in my case it was 5oz):
- sifted self-raising flour (less one heaped tablespoon)
- caster sugar
- margarine
- one heaped tablespoon of cocoa powder
- one teaspoon baking powder

Method:
1. Turn on the slow cooker to Low while you're prepping the ingredients.
2. Mix/beat all the ingredients together, having sifted in the flour and baking powder.
3. Line the cooker pot with two cake baking liners (not sure if necessary but thought it might prevent any burning round the edges).
4. Spoon the cake mixture into the liner, in the pot and level off.
5. Turn up to High and put the lid on. (There's some discussion about putting a tea towel under the lid to catch moisture but I didn't do this - I wanted to see it cook through my glass lid!). I took the lid off for the last 10 mins or so.

Time: It was cooked in 1 and half hours (14.50 to 16.20).
 

Review:
Unfortunately, when I lifted the lid off at about 15.55 to skewer it to test readiness, the very middle of the cake collapsed! However, it tasted excellent - moist and chocolatey - and didn't affect the taste at all, it just looked a bit skew-whiff!  Some decoration soon took the attention away from it. The kids scoffed the cake happily!  It would delicious still warm with some custard, or cream of ice-cream.

Next time I might increase the mixture to a 3 egg one to make a more substantial cake. In which case I'll have to experiment with time again, perhaps increasing it by 20 mins (?) and not taking the lid off beforehand!