Spray a large saucepan liberally with nonstick cooking spray. Heat saucepan over medium-low heat. Add onions and garlic, and sauté until clear, mixing constantly so they don’t burn.
Add asparagus and six to eight cups water (depending on your preference of thickness. I usually start with six and add more if necessary). Raise heat and bring to a boil. Add soup mix, salt and pepper. Cover and cook about 25 minutes, until asparagus is tender.
Add yogurt and puree with hand blender until smooth.
To clean green asparagus from insects, the tips as well as the triangular side leaves should be cut off and discarded. Alternatively, use frozen, thawed asparagus with a reliable hechsher.