Make It:

I made this with leeks, carrots, and turnips, since those were what I had on hand, but it would adapt very easily to almost any combination of root veggies, white and/or sweet potatoes, and some type of onion.

Wash, peel, and cut the veggies into pieces that are somewhat uniform in size.  Toss with some olive oil and roast in a large roasting pan at 425 degrees, until they start to soften and caramelize.  Turn the veggies about every 10 minutes.  The leeks/onions will take about 20-30 minutes, the turnips/potatoes about 40 minutes, and the carrots about 45-60 minutes.  (All the measurements are approximate.  My roasting pan was filled, with about 2/3 carrots and 1/3 each leeks and turnips.)

As the veggies finish roasting take them out and put them in a soup pot.  When they are all in the pot, cover with stock and bring to a simmer, then simmer for about 30 minutes or until the veggies are all tender.  Puree with an immersion blender or in a blender or food processor.  Whisk in about 3/4 cup creme fraiche.  Season with salt and pepper.

To serve the soup, ladle into individual bowls, and put a spoonful of the remaining creme fraiche on top.  

I think Vermont Butter and Cheese makes creme fraiche, or you can make your own with Butterworks Farm heavy cream and cultured buttermilk:  Heat 2 cups heavy cream and 1-2 tablespoons cultured buttermilk to 85 degrees, pour into a glass jar, partially cover and leave at room temperature for 8-24 hours, until thickened.  Stir and refrigerate for another 24 hours before using.  It will keep for about 2 weeks in the refrigerator.