Chocolate Butter Cream. Ideal for decoration and layering in the cake!!!

Prague Cream!
The recipe is completely according to GOST !!!
Ideal for Prague cake and decoration of various desserts: cupcakes, eclairs, choux, brioche...
I prepared this cream for a very tasty cake in a glass or cake to go. There is a video on how to make these desserts on my channel!
For cream:
1 yolk
20 grams of water
140 grams of white condensed milk (if you want a cream that is softer in consistency, then add 170-180 grams of condensed milk, but such a cream will be more tender for decoration.
10 grams of cocoa powder tasty and high quality
200 grams butter 82% fat