We love the scent of the curry leaves in this southern Indian-style dish; they are available fresh and frozen.
Melt butter with oil in a large straight-sided skillet over medium-high heat. Add cumin and mustard seeds. When mustard seeds begin to pop (about 30 seconds), add curry leaves (take care, as mixture will splatter) and asafetida. Fry 30 seconds.
Add onion, garlic, chiles, and 1 teaspoon salt. Cook, stirring occasionally, until onion is translucent, about 3 minutes. Add tomatoes and turmeric and cook, stirring occasionally, until tomatoes are softened and beginning to caramelize around the edges of the pan, 3 to 5 minutes. Stir in 1/4 cup water and scrape up any browned bits. Add rice and stir to coat. Cover, remove from heat, and let stand 5 minutes. Taste and adjust seasoning with salt if needed. Serve, sprinkled with cilantro.