Add olive oil to a large saucepan and heat over medium.
Place celery and onion in the saucepan. Stir and cook until the celery is almost tender, about 5 minutes.
Add chicken broth, garlic salt, butter flavoring, parsley, celery seeds, and black pepper and bring to a boil.
Lower the heat, cover with a lid, and simmer until the celery is fully soft, about 5 to 10 minutes.
Remove the saucepan from the heat.
Add milk and potato flakes to a mason jar. Secure the lid and shake until the potato flakes dissolve in the milk.
Pour the hot celery mixture into a blender, filling it no more than halfway. Hold the lid down and pulse a few times, then blend until smooth. Repeat as needed.
Pour the blended soup back into the saucepan.
Heat the soup on low. Add the milk and potato mixture, stirring until everything is combined and hot, about 3 to 5 minutes.
Notes
3 WW Points4 Smart Points (Old)
Tips and Tricks
Blending - Use caution when blending hot liquids. Always fill your blender only halfway and hold the lid down with a towel to prevent spills.Texture - Control the thickness. Add more broth if you want a thinner soup, or use a few extra potato flakes for a thicker consistency.Seasoning - Taste before serving. Adjust garlic salt and pepper at the end as needed.
Storing and Reheating
Reheat on Stovetop - Place a serving in a saucepan with 1 to 2 tablespoons water. Warm over low heat, stirring until creamy. Store any leftover soup in an airtight container in the refrigerator for up to 3 days.