Original recipe uses Nutella fillings but I thought it'd be as nice with Peanut Butter so I tried both (or even mixed both inside one mochi); and they turned out ... wow...!!
1&1/2 cups Sticky-Rice Flour
1&1/2 cups Water
1/2 cup Sugar
1/2 cup Cacao Powder
1) Mix the flour with water and microwave for 5mins
2) In a seperate bowl, mix the sugar and cacao powder
3) Add the cacao mixture (in 2/3times) to #1 and mix well until smooth and chocolately colored
4) Put #3 back in microwave for another 5mins
5) When #4 is done, let it rest for about 10mins or until its slightly cooled
6) Flour your hand & plate to minimise the stickiness of the dough when forming the mochi
7) Take a scoop of mochi dough, flatten it like a pizza base, put about a teaspoon of nutella or peanut butter in the middle and fold the ends together to form a ball shape.
Note 1: If possible, harden the nutella in fridge before use would make your life easier when forming the mochi
Note 2: I couldnt free my hands to take any pix while struggling with the sticky-messy dough, but do trust me that its all worth it... kekekeke