Chop the cashew nut into small pieces and keep aside. This recipe uses raw cashews but if you prefer roasted ones, go ahead and roast some and use in the halwa.
In a bowl, combine the corn starch, 1 ½ cups of water and food coloring and whisk it well to dissolve completely. Make sure that there are no lumps in the mixture. Using a whisk really helps in mixing it together to form a lump free batter.
In a pan, add the sugar and the remaining one cup of water and bring it to boil. Once the syrup boil vigorously, add the lemon juice and mix. Let the syrup boil for a minute more to thicken slightly. There is no specific consistency that we need to watch for. Just boil until it is slightly thick and syrupy.
Now slowly pour the prepared corn starch mixture and mix well. Make sure to keep mixing as it will start to thicken in the bottom right away.
Keep mixing and once the halwa thickens slightly, add a TBSP of ghee and mix until the halwa absorbs it.
Now add the cashew nut and the cardamom powder and mix well.
At regular interval, keep adding the ghee and cooking the Karachi Halwa, until it all comes together as a lump.
You will notice that by the time we use all the ghee, the halwa has become vert glossy and it no longer takes in the ghee as readily as before.
This is stage we need to pour the halwa in the prepared pan.
Once you pour the halwa, smooth the top and let it set for at least an hour.
Once the Bombay Karachi Halwa has set, invert it on to a tray and cut into desired size pieces.