Saute celery in olive oil in a heavy soup pot until soft.
Add scallion and asparagus, and continue to saute until vegetables are soft.
Add stock, garlic mustard, and Dijon, and simmer medium-low for 15 minutes.
Go to it with your immersion blender.
Stir in butter until melted and incorporated into the soup. Add salt and pepper to taste.
Serve warm, topping each bowl with a Tbsp of toasted sunflower seeds.