How to Make It
In a 4-quart enameled cast-iron casserole, heat 2 tablespoons of the oil. Add 1 of the onions and cook over moderately high heat, stirring occasionally, until softened but not browned, about 4 minutes. Add the peppercorns and turmeric and cook, stirring, until fragrant, about 1 minute. Add the water, rice and salt and stir well. Bring to a boil, then cover tightly, reduce the heat to low and cook for 15 minutes.
Meanwhile, in a large skillet, melt the butter in the remaining 1 tablespoon of oil. Add the cashews to the skillet and cook, stirring constantly, until golden brown, 4 to 5 minutes. Using a slotted spoon, transfer the cashews to paper towels, leaving as much oil behind as possible. Add the remaining onion and cook over moderate heat, stirring constantly, until it turns deep brown, about 8 minutes. Add the browned onion to the cashews.
When the rice is cooked, stir in the frozen peas. Cover until the peas have warmed through, about 3 minutes. Turn the rice into a bowl and garnish with the onion and cashews. Serve immediately.