Cook onions for about 5 minutes, stirring occasionally. Add garlic and cook 1-2 minutes, until fragrant.
Add celery, potatoes and bay leaf, and pour in broth until it just covers the vegetables. Add water, if needed. Cover and bring to a rolling boil.
Turn down heat and simmer until the potatoes are cooked, about 10 minutes.
Turn off heat, remove bay leaf and add the fresh herbs. Carefully ladle soup into a blender or use an immersion blender. Blend until smooth. Salt and pepper to taste.
Top soup with a dollop of sour cream or Greek yogurt, if desired. For an extra kick, add a few drops of hot sauce or sriracha.