In a large saucepan combine celery root, garlic, and 2 tsp. kosher salt. Add enough water to cover. Bring to boiling. Reduce heat; simmer, covered, for 12 to 15 minutes or until very tender; drain.
Puree mixture with the cream and butter in a food processor until smooth. Season to taste with additional salt and some pepper. If desired, top with additional butter and celery root leaves before serving.