1/2 onion
4 green chillies
1 tablespoon butter
salt
1. Thaw spinach in the microwave according to package directions. (It doesn't have to thaw completely).
2. Put the (partially) thawed spinach and the rest of the ingredients in a sauce pan and cook on medium heat until done (~10 minutes), covered.
3. Take the chillies out and use a blender or stick blender to puree.
4. Add butter