The lime isn’t traditional, but I think it adds a nice punch. You can omit it if you plan on keeping the sauce in the fridge for a while. I put the spinach and cilantro into the food processor directly after washing it, so there was some extra moisture. If you have a hard time pureeing until smooth, add a tablespoon of water and see if that does the trick.
Ingredients: 1 ½ cups tightly packed baby spinach leaves,2 cups roughly chopped cilantro leaves and stems (about 1 bunch),½ teaspoon coriander,½ teaspoon cumin,2 cloves garlic,¼ cup olive oil,¼ teaspoon salt,1 serrano chile, (seeds and all) roughly chopped
Instructions: Combine the first 8 ingredients in a small food processor or blender and puree until smooth, adding water if necessary. If eating immediately, add the lime juice. Otherwise, transfer to an airtight container and keep in the fridge for up to a week.