Defrost koya to room temperature. Crumble it well and add to a heavy bottom nonstick pan.
Heat it on a very low flame constantly stirring to prevent burning
When the koya gets warm, add sugar, cardamom powder rose water. you could increase the flame to medium
Within a short while , sugar melts and the mixture turns to a halwa like consistency.
Continue to cook stirring constantly,till it begins to leaves the sides of the pan and becomes thick like a mass. It must not be runny like halwa. Let the mix cool down completely.
Divide the mix to 2 parts, knead one of them to a smooth dough, shape to a square on the greased foil.
Add cocoa to the other part, Knead gently with greased palms till the dough looks soft.
Place this over the first layer, sprinkle nuts. gently press if needed, but the layers stick on their own. Freeze it for 10 mins or refregerate for about 30 minutes.Cut chocolate burfi to desired shapes.
Use up chocolate barfi with in 2 days, keep refrigerated.