In a bowl mix 1 cup of water with the corn starch and food coloring, mix well until smooth.
In a no stick pan on medium high add the remaining water, white sugar and brown sugar. Stir well until sugar is fully dissolved. Once small bubbles have started to form (not a full boil) add the corn starch mixture.
Stir constantly until it just starts to thicken then add the oil. Stir well. Reduce heat to low. Stir for 30 seconds every 15 minutes adding 2 tablespoons of butter/ghee each time to incorporate. (Do not over stir) It will take about 1 hour and 30 minutes or so for the Halwo to become very thick and a lot of tiny bubbles will form.
When that happens add the cardamom powder, nutmeg and nuts (if using). Stir well and pour the Halwo into a dish/cake pan. You may use a very small cake pan that is 6" X 9" for a thick halwo. It will fill that size pan to the top.
Let cool on unrefrigerated, 3 hours for the small pan. Once fully cooled, turn pan upside down onto a plate and the Halwo will slide out.