Bring 1 1/2 cups stock and butter to a boil. Stir in rice and cover, reducing heat to a simmer.
In a food processor, process 1/4 cup stock, spinach, cilantro, jalapeño or serrano and scallions into a thick paste. Scrape into a bowl, rinse out processor bowl and return it to the base.
Combine ancho and remaining 1 1/4 cups stock in small pot and bring to a boil. Reduce heat to low and simmer to soften the pepper. When soft, process pepper and stock with fire-roasted tomatoes. Place tomato paste in the pot the ancho and stock were cooked in and stir 30 seconds over medium heat. Stir in the ancho-tomato sauce, season with pepper simmer and thicken 12-15 minutes.