Set a roasting pan halfway filled with water on the floor of the oven. Set a rack in the center and preheat the oven to 225°.
Meanwhile, in a large bowl, whisk the eggs until very well mixed and airy, 30 seconds to a minute. Set aside.
In a small, heavy-bottomed saucepan, combine the jaggery, cardamom, and cloves. Cook over medium heat, stirring frequently, until the jaggery melts and bubbles. Remove from the heat, and taking care to avoid splatters, whisk the coconut milk into the hot mixture. Continue to whisk until smooth, then strain to remove the cardamom and cloves.
Whisk the eggs well once more, then slowly drizzle the jaggery mixture into the eggs, whisking constantly and rapidly to keep the eggs from curdling. Strain the mixture again if necessary to get rid of any excess foam. Stir in the vanilla, nutmeg, and a pinch of salt, and divide the mixture evenly between four 6-ounce ramekins. Transfer them to a shallow roasting pan and pour enough warm water into the roasting pan to reach about 1 inch up the sides.
Transfer to the oven and bake until the custards look set but still jiggle slightly when shaken, 50–60 minutes. (You can test for doneness with a toothpick, which should emerge clean.) Remove and immediately top each portion with two cashew halves. Let cool and serve at room temperature or chilled.