Place a medium or large pot over medium-high heat,then add the butter.
Once it's completely melted, add and saute the onion until it softens.
Add the ground allspice and cook for at least a minute, mixing
Cook for a couple of minutes, mixing continuously.
Add all the vegetables and some salt, then mix to coat everything.
Cover with a lid, lower heat, and simmer for about thirty minutes, or until the vegetables are soft --- remember to stir occasionally.
Pour the stock and add the bay leaf.
Place the lid back, turn up the heat, and bring it to a boil.
Lower the heat and continue simmering for twenty minutes.
Take the pot off the heat and set aside until it cools down.
Remove the bay leaf, then use an immersion blender to puree the vegetables --- until you get a smooth texture.
Put your celery and potato soup on the stove and set it to medium heat.
Add ground white pepper and pour the cream.
Mix to combine everything, taste and adjust seasoning, then cook for about two minutes (just enough to warm it up).
Transfer your creamy celery and potato soup into serving bowls, sprinkle with parsley, if preferred --- then enjoy!