Chocolate Banana Muffin

I found a lot of new recipes recently. This is the first one i wanted to try because i am looking for temptation from the chocolate-banana combination.
I had to put on halt all the preparing work when i suddenly found something worth remembering. A twins egg, the first one in my baking journey, I nearly scream out of excitement ;p So, of course everything needed to be put aside for a photo session.

The muffin rise higher than expected eventhough the recipe do not call for baking powder. Chocolate Banana Muffin Recipe (adapted from 孟老师的100道小蛋糕)
Banana 70g，Sweetened condensed milk30g, butter 65g，Icing sugar50g，egg yolk 1, cake flour 90g，Chocolate powder 10g，Baking soda 1/8tsp，
1）Crush banana, add in condensed milk
2）Add icing sugar into soften butter and mix.
3）Fold the egg yolk into mixture 2 and mix well.
4）Add 1 into mixture and continue mix
5）Sieve all the powder and stir in the mixture
6）Pour the mixture into muffin cup up to 70% full.
7）180c bake for 25-30min