In a small pot, bring ½ cup water to a low boil. Add the frozen green beans, return to a boil, lower the heat to medium-low, and cook for 7 to 9 minutes, until tender.
Transfer the cooked green beans, along with the cooking liquid, to a blender. Process until smooth, scraping down the sides as needed.
Transfer to a small bowl, let cool, and then serve or store until ready to use. Store in an airtight container in the refrigerator for 3 to 5 days or in the freezer for 4 to 6 months.