Put the cilantro, spinach, and broth in a blender and puree.
Add the milk and salt, and blend until well combined.
In a medium non stick skillet with lid, over medium heat, warm the olive oil and butter.
When the butter is melted, add the rice and sauté, stirring about every 30 seconds, until it just begins to brown, 3 to 4 minutes.
Add the onion and garlic and cook 1 minute, stirring constantly.
Add the contents of the blender, stir well, turn the heat to high, and bring to a boil.
Cover the pan, turn the heat to very low, and cook for 20 minutes.
Stir the rice carefully to avoid crushing it, cover and cook another 5 minutes.
Take the pan off the heat and let the rice steam in the covered pot for 10 minutes.