Cha Gao, or Pu-erh Tea Paste in English, was first produced in the Tang Dynasty. Cha Gao is made using Pu-erh tea leaves. One kilogram of tea leaves can only produce around 200 grams of Cha Gao.
You only need to use 1 piece for every 150ml of water. This should be good enough for 2 to 3 infusions.