Grease a baking dish and set a aside.
In a deep heavy pot, bring the sugar and 3½ cups of the water to aboil.
In a bowl, whisk the cornstarch and saffron with the remaining 1/2 cup water until smooth.
Reduce the heat to medium. Slowly pour the cornstarch mixture into the pot, whisking constantly to prevent lumps.
Cook, stirring constantly, until the mixture thickens.
As the mixture turns thick, start adding ghee/oil tablespoons at a time, stirring well after each addition. Add more whenever the halwa sticks to the bottom of the pot.
Keep stirring until the oil separates and the halwa turns glossy, thick, and pulls away from the sides of the pot.
Stir in the cardamom, cloves, nutmeg.
Pour into the prepared dish and spread evenly, about ½ to 1 inch thick.
Put the halwa on a baking sheet.
Let cool 2 to 3 hours until firm, then cut into squares and serve.