Heat the butter in a 3-quart saucepan over medium heat. Add the onions and celery and cook until they're tender.
Stir the broth, black pepper and potatoes in the saucepan and heat to a boil. Reduce the heat to low. Cover and cook for 15 minutes or until the potatoes are tender.
Place half of the broth mixture and half of the milk into your Blendtec or Vitamix and secure the lid.
For Vitamix: Start on VARIABLE speed #1. Turn machine on and slowly increase speed to VARIABLE, speed #10/HIGH. Blend for 10 seconds using the tamper to press the ingredients into the blades.
Pour into bowl and repeat with remaining broth mixture and milk.
Serve immediately.
All done! Enjoy!! Now take a photo, rate it, and share your accomplishments! :) Tag @BlenderBabes & #BlenderBabes
Notes
For a garlicky variation, try adding 4 cloves of garlic to sauté at the beginning.