Remove the roots and most of the green stems from the scallions, then trim and remove seeds from jalapeno if using.

Put all of the ingredients into a blender and make a puree. Pour puree into a medium saucepan over medium heat and bring to a gentle boil. You should see a few bubbles but not much more. Remove the pan from the heat and allow the sauce to cool before storing or using it right away according to the recipe.