Have the stock ready to go whether you make it yourself, buy it canned or reconstitute the stuff I like.
Peel and quarter the sweet potatoes.
Leeks - You are only going to use the white and tender green parts of the leeks so cut the hairy tip off the root as well as the dark green leafy top which by the way would be a great ingredient for your own veggie stock. Leeks can be full of sand so you want to cut them up into ¼ inch slices, separate the rings and give them a good washing in a colander under cold running water.
Ginger - Peel and grate the ginger. I use a spoon for peeling and my Microplane grater/zester. Works great for these types of jobs.
In a pot big enough to hold all these ingredients (I used a 4 ½ quart sauce pot that worked fine), add the stock, sweet potatoes and leeks and bring to a boil over medium high heat. Once at a boil, reduce heat, cover and simmer until the potatoes are fork tender, about 20 minutes.
When done, remove the pot from the heat and let it cool some before attempting the pureeing.
2) Here you can use a blender or food processor and work in batches to puree the potatoes, stock and leeks. I prefer to use my hand blender to minimize the cleanup and avoid the mess from spilling during transfer. Whatever method you use, you want the ingredients to become a smooth puree.
3) Before you finish, add the pepper, cayenne and ginger and puree some more. If you used a blender or food processor, pour the soup into a large bowl and let cool. Since I used a hand blender, I just left everything in the pot.
4) Once the soup becomes lukewarm, add the heavy cream and stir to mix well. Here's a good time to taste and adjust the seasoning with a little salt and I can almost guarantee it will need salt to boost the flavor.
5) Cover and refrigerate for at least 4 hours until the soup is well chilled.