Place the cashews in a blender with the corn starch and blend until a very fine powder forms. There shouldn't be any cashew pieces. Be careful and do this slowly because any nut, when overly processed, can turn into nut butter.
Place the sugar and water in a saucepan and let it come to a boil. Lower the heat to simmer, add the cardamom and saffron, and let the syrup cook about five minutes. Check it regularly to see if it has achieved a one-thread consistency. What this means is that when you place a drop of the hot sugar syrup on the tip of your thumb and touch the tip pf your forefinger to it, the syrup should pull up in a short thread as you separate the thumb and forefinger. If that is too complicated just get yourself a candy thermometer and take the syrup off the heat when the temperature reaches 225 degrees Fahrenheit/110 degrees Celsius.
Heat a nonstick wok or skillet over low heat. Add the cashew powder and cook, stirring, about two minutes or until it is warmed through. Then add the sugar syrup to it. Turn heat to low and continue mixing the mixture with the ladle. Eventually, in a couple of minutes, the mixture will thicken and will start pulling away from the sides of the pan, and will achieve a wet-dough-like consistency.
Turn out the cashew paste on a clean surface, rub some oil on your palms and fingers, and knead the paste a few times until it looks really smooth. Be very careful because the paste is still hot.
Pat the cashew paste into a greased plate or tray and spread it evenly. You can also do this with a rolling pin if the mixture is still hot to handle. The layer should be about a third of an inch thick.
Set the plate aside to cool completely for two hours. Use a sharp knife to cut into diamond shapes.