Grease a 8 inch square pan with ghee or line it with parchment paper. This will make it easier to remove the burfi once it's set. Set it aside for later.
Add the raw pistachios to a small grinder jar and pulse to grind into a fine powder. Make sure that the pistachio powder does not become oily(can happen if you grind for long on high speed). You can leave some bits slightly coarse if you like- this will add texture in the burfi.
In a heavy-bottomed, non stick pan, add the butter, milk and sugar. Stir gently and let sugar dissolve over low medium heat. When the sugar is undissolved, you will feel that the mixture feels thickish to stir. It will be easier to stir after the sugar has melted.
Cook for 1-2 minutes until the mixture starts simmering.Then, add pistachio nut butter. Mix well to incorporate with the milk & sugar mixture. Our wet ingredients are ready!
Next, add the dry ingredients - milk powder and pistachio powder. Also add the green cardamom powder, rose water and green food color. Stir everything using a soft spatula to mix very well. The mixture will feel quite thick.
Cook the burfi mixture for next 4-5 minutes on low medium heat. The mixture will need bit of arm strength to stir. If the mixture gets stuck to sides of the pan and gets too dry, leave it(don't mix back).
When the mixture starts clumping around the spatula and you are able to fold it over itself, it's the right consistency. Switch off the stove. Do not over cook else the burfi will become sticky. You can test by taking a small portion and rolling it into a ball—it should hold shape and should not stick to your fingers.
Immediately transfer the pista burfi mixture into the lined pan. Using a spatula, press it down evenly. Garnish with some chopped pistachios on top for a decorative finish. Press down the pistachios you added on top so that they stick.
Let the burfi cool down and set for 1 hour at room temperature, and then place it in the fridge for 2-4 hours for setting.
Once cooled you can decorate it with edible silver leaf (warq). Using a sharp knife, cut it into square or diamond-shaped pieces. Wipe the knife between cuts for neatness. Your pista burfi is ready to serve!
Serving & Storage - Store the burfi in an airtight container and keep refrigerated for a up to a week. Burfi will be slightly hard straight out of the fridge (due to hardening of butter), let sit at room temperature for 10-15 minutes before serving.