Pulse onion, carrots, celery and garlic in food processor until the pieces are less than 1/2 inch. Alternatively, dice veggies into small pieces. Set aside. Separately, chop potatoes and rinse with cold water.
If using Instant Pot:
Melt butter on saute mode. Add onion, carrot, celery, garlic mixture and allow to cook, stirring only to prevent burning, until slightly golden brown. About 5 minutes. Add potatoes, broth, bay leaf, pickles and pickle juice. Close lid and cook on high pressure for 12 minutes. Quick or natural release the pressure. Remove Bay leaf.
If cooking on stove top:
Melt butter in heavy bottom stockpot. Add onion, carrot, celery, garlic mixture and allow to cook, stirring only to prevent burning, until slightly golden brown. About 5 minutes. Add potatoes, broth, bay leaf, pickles and pickle juice. Bring to a boil and then reduce heat to maintain a simmer. Cook until potatoes are very tender, about 30 minutes. Remove Bay leaf.
If making in on slow cooker:
Melt butter in heavy bottom stockpot. Add onion, carrot, celery, garlic mixture and allow to cook, stirring only to prevent burning, until slightly golden brown. About 5 minutes. Transfer to slow cooker and add potatoes, broth, bay leaf, pickles and pickle juice. Cook on high 1-2 hours or low 4-8 hours. Remove Bay leaf.
To blend soup:
Use an immersion blender to partially blend while still maintaining some chunks. Alternatively, you can add about half the soup to a blender and blend until smooth, then combine with remaining soup. Stir in heavy cream and fresh dill. Taste and add additional pickle juice and/or salt, if needed.