Rinse carrots, pat it dry ,trim the edges , peel the skin , grate and keep it aside
In a heavy bottom thick pan /kadai (don't use Nonstick), add 2 tablespoon of ghee/clarified butter and add grated carrot, 
Saute the carrot till the rawness of carrot goes,it takes around 6-8 minutes.
Now add boiled milk and let the carrots cook in the milk. Cover lid and cook on low flame .
When carrot is completely cooked, open lid and cook until milk reduces. 
Once milk is almost reduced to 90% , add sugar , mix well and let it continue to cook on low flame
Whilst, heat 4 tablespoon of ghee and fry all chopped nuts until it turns golden in color. Add raisins at last and remove from stove.
To carrot halwa , add cardamom powder , fried nuts , raisins along with ghee.
Mix well ;  when everything comes together leaving the pan from edges ,  gajar halwa in ready. 
Serve Carrot Halwa hot, warm or cold .Can also serve with Ice cream.