In a dutch oven or a large shallow pot melt butter over medium heat and add onions, garlic, salt, pepper, and celery for about 5-7 minutes until the onions are translucent and the celery is soft.
Add flour, mix well and cook for another minute.
Add the chicken stock. stir, and turn up heat to bring to a boil. Lower heat and let simmer, uncovered, for 15 minutes.
With an immersion blender, regular blender, or food processor blend until mostly creamy.
Store in an airtight container in fridge for up to 3 days or freezer for a month.