Melt 1 generous tablespoon of butter in a large saucepan or Dutch oven over a low/medium heat. Finely dice the onion, thinly slice the garlic and finely chop the celery. Add to the saucepan and stir well. Sweat gently for a few minutes until tender.
Add the cauliflower florets to the saucepan. Thickly slice the pickles into discs and add to the saucepan. Add ¼ cup pickle juice from your pickle jar and the stock. Stir well to combine. Bring to a boil, then reduce to a simmer. Simmer for 10 minutes to soften the cauliflower and pickles. You may add salt and pepper if desired; this will depend on the strength of seasoning in your stock.
Remove the soup from the heat and carefully use a handheld stick blender to process the soup to a smooth purée. Alternatively, you can allow the soup to cool a little, then transfer to a free-standing blender to process. Taste the soup and adjust seasonings as desired. Divide the soup between individual serving bowls. Stir a tablespoon of sour cream through each bowl and scatter with chopped fresh dill to serve. Serve alone or with Keto bread for dipping.