How to Make It
In a large, deep skillet, heat the olive oil until shimmering. Add the onion, tomatillo, garlic and a generous pinch of salt. Cook over moderate heat, stirring occasionally, until softened and just starting to brown, about 7 minutes. Stir in the cumin and cook until fragrant, about 1 minute. Add the tomatoes, chiles and stock and bring to a boil. Simmer over moderate heat, stirring occasionally, until the liquid is reduced by half, about 20 minutes. Transfer the sofrito to a blender or food processor and let cool slightly, then puree until smooth.
Wipe out the skillet and cook the sofrito in it over moderate heat, stirring, until hot, about 5 minutes. Gradually fold in the rice and cook just until it is hot and coated in the sofrito, about 5 minutes. Season with salt, garnish with cilantro and serve.