After making corned beef for St. Patrick's Day, I was left with some gorgeous broth. That, a bulb of celeriac and a hunk of smoked Gouda inspired this velvety-rich soup that gets an extra kick of smoky intensity from pimentón. I've made the addition of a little heavy cream optional; it's not necessary but it is delicious! —gluttonforlife
Roughly chop the celery root and potato, then combine with onion and beef stock in a medium-sized, heavy saucepan over medium-high heat. Simmer until vegetables are very tender, at least 30 minutes.
Cool slightly before pureeing in food processor, or with an immersion blender. Return to same pot over medium heat and stir in cheeses, cream (if using) and pimentón. Add salt, if needed. Garnish with chopped walnuts.