Brown the sausage in either butter or olive oil before you soften the leeks and fennel. Remove the sausage and set aside, and use the pan drippings to saute the leeks and fennel later. (I used apple sausage from the farmers market - just made the day before from a local farm and it was awesome. Would also work well with any kind of flavored sausage like sage or Italian. ) Continue on with the recipe, and add sausage after you've blended the ingredients together so that your sausage doesn't have the consistency of applesauce and you can get a spoonful of meat with each bite.
As for the potatoes, I didn't have Russet potatoes so I used a "medley" I had from Trader Joe's that included purple potatoes, red potatoes and fingerlings. It worked just as well.
I used an immersion blender because the recipe said it would work better, but I think you'd have more control with a blender or Cuisinart. I like more "chunk" and less puree for this soup.
We skipped the croutons in favor of some crunchy bread. I had some ciabatta rolls which I cut in half and spread butter over. Add a sprinkle of Asiago and Parmesan cheese over top and place in toaster oven until crispy. You can cube them and use as croutons or as bread on the side.
Enjoy and stay warm, ladies and gents!