How to Make It
In a skillet, toast the cardamom, star anise, coriander and cumin over moderately low heat, stirring, until fragrant, 2 minutes; transfer to a spice grinder and let cool completely, then coarsely grind.
In a saucepan, heat the canola oil. Add the garlic and ginger and cook over moderate heat, stirring, until lightly golden, 3 minutes. Add the ground spices, turmeric, sugar and 1/2 teaspoon of salt and cook, stirring, for 30 seconds. Add the coconut milk, fish sauce and saffron, bring to a boil and simmer for 5 minutes. Cover and let stand for 15 minutes. Strain the curry sauce and return it to the pot. Stir in the lime juice and basil; keep warm.
In a bowl, combine all of the ingredients except the grapefruit and mint; let stand for 15 minutes. Carefully peel the grapefruits, removing all of the bitter white pith. Working over the bowl, cut in between the membranes to release the sections. Stir in the mint.
In a large nonstick skillet, heat 2 tablespoons of the canola oil. Season the scallops with salt, add half to the skillet and cook over moderately high heat, turning once, until just barely cooked through, 5 minutes; transfer to a plate. Repeat with the remaining oil and scallops.
Serve the scallops with the grapefruit salad; drizzle with some of the curry sauce, garnish with the cashews and serve.