For the basmati rice: Melt the butter in a saucepan over medium heat. Add the onions and cook, stirring occasionally, until softened, about 5 minutes. Add the rice and cook, stirring, until well coated, about 1 minute. Add the chicken broth, 1 1/2 cups water, 1/2 teaspoon salt and some pepper. Increase the heat to medium-high and bring to a boil. Cover, reduce the heat to low, and cook until the liquid has been absorbed, about 12 minutes.
Remove from the heat and let stand, covered, for 3 minutes. Stir in the cilantro and season with salt and pepper.
For the chicken sambal: Whisk together the ponzu, sambal, brown sugar and fish sauce in a small bowl. Set aside.
Sprinkle the chicken breasts and thighs liberally with salt and pepper on both sides.
Heat the coconut oil in a large Dutch oven over medium-high heat. In two batches, add the chicken, skin-side down, and sear until golden brown, about 6 minutes; flip and sear on the reverse side, another 2 minutes. Transfer the chicken to a plate.
Reduce the heat to medium and stir in the onions, garlic, lemongrass and galangal. Saute until the onions have softened and the garlic, lemongrass and galangal are lightly toasted, 5 minutes. Add the crushed tomatoes and the sambal mixture; bring to a boil, then reduce the heat to a simmer. Return the chicken to the pot, skin-side up, and simmer for 20 minutes to finish cooking through.
Serve over the rice, garnished with lime wedges, scallions and cilantro.
This dish is great to make ahead, as it gets better as it sits. Cool the chicken and sauce completely before storing in an airtight container. When ready to reheat, turn the broiler on high. Place the sauce in a large ovenproof skillet, then add the chicken skin-side up. Simmer until heated through, about 15 minutes, then lightly brush the chicken skin with oil and place the pan under the broiler to crisp the skin.