Heat ghee in a non stick pan on low heat.
Add milk to it and mix well.
Add milk powder to the milk and mix well on low heat.
Mix well on low heat.
Now add sugar.
Sugar will melt and mixture will become liquidy.
Now add crushed walnuts. Mix well.
Now put heat to medium and stir the mixture continuously.
After 5-6 minutes, the mixture will come together and start leaving the edges of pan. Add vanilla essence to it and mix well. The mixture will come together like a dough.
Now take and greased pan ( I have used 8" by 8" square tin). Transfer the mixture to the greased pan and press it evenly with spatula.
Keep it aside.
Now take dark chocolate. (you can use milk chocolate too).
Melt the chocolate in microwave for stirring in between. (If melting chocolate in microwave, always put first for 30 sec and then check, if not melted place further for 30 sec and check. Do not melt by keeping the chocolate for long time as it tends to burn).
Now pour the melted chocolate on the top of the mixture in the pan. Move the pan gently to all the sides. The chocolate will spread easily on all the sides.
Cover the pan and keep it to set for about and hour. Then cut into desired shapes.
The chocolate walnut burfi is ready to serve. The burfi can be refrigerated for a week in an airtight container.