This delicious soup can be made vegan (by omitting the cream and using veggie stock), and is the perfect accompaniment to those "first-sweater-nights" in early Fall.
Turn your oven to 375 and get out two baking sheets.
Rinse and chop your leeks and fennel and toss with just a little oil, salt and pepper. Place on one baking sheets. on the other, scrub and cut up your potatoes and kohlrabi to roughly the same size (about half the size of your fennel pieces), and also toss with oil, S & P.
Roast for 15 minutes, with the potatoes on bottom and fennel in middle of the oven, then toss. Roast for 15 more minutes. Remove from oven and add to large soup pot.
Turn heat up on soup pot and begin to add in the warm stock. Bring to a boil, then let simmer for 10 minutes.
Remove from heat, and purée (a Vitamix or a blender in batches is easier than an immersion blender.) Pour back into soup pot, and with the heat off, stir lemon juice first, and then cream (or additional water to thin it to desired consistency). Optional to pass it through a fine mesh sieve to remove solids. Serve garnished with minced thyme and minced fennel fronds.