Heat a large pot over medium heat. Add the bacon and begin cooking.
After about 2 minutes, add the garlic and leeks. Continue to cook for about 10-12 minutes. The leeks should have begun to sweat and reduce in size. They may start to colour slightly.
Next, add the potatoes and stir to coat in bacon fat and mix thoroughly with the leeks. Add the rosemary, cumin, and pepper.
Add the stock, and increase the heat to medium and bring up to a rolling simmer. Add the parmesan rind if using.
Simmer until the potatoes are cooked through and the leeks are very soft, about 30 minutes. If the soup becomes too thick, add water a 1/2 cup at a time.
Once everything is fully cooked and soft, remove from the heat. Remove the parmesan rind.Blend with an immersion blender until very smooth. (Cool slightly before blending in a traditional blender.) Add the cream, and blend to combine. Season with salt to your tastes. Serve.
This soup freezes well in an airtight container for up to 3 months.