In a large dutch oven or heavy stock pot, heat oil or butter and heat on medium high until shiny/melted - about 35 seconds.
Add leek, carrots, celery, and onion.
Cook until softened and lightly browned, about 6 minutes, stirring occasionally to prevent burning.
Add garlic and continue to brown vegetables until garlic is soft and fragrant, about 2 minutes.
Add diced pickles, stir. Set pickle juice aside - do not drain.
Add marjoram, potatoes, salt and pepper, stir.
Add in pickle jar juice and stock and bring to a boil.
Optional: for traditional Polish flavor, add chicken or pork bones to soup while boiling (remove before serving, this is just for additional hearty flavor).
Let soup boil until slightly reduced and potatoes are soft.
Lightly mash potatoes in soup with back of a spoon or a potato masher, there should still be chunks - but we want slightly smashed boiled potatoes for a lovely thick soup.
Stir well to mix.
Turn stove off.
Stir in cream, whisking to combine as it is added.
Return heat to pan and bring back to boil.
Reduce heat and let thicken, about five minutes.
Serve with thin slices of pickle and fresh minced dill.