celery root (celeriac), about 1 3/4 to 2 lbs (800 to 900 grams) • Golden Delicious apples • onion • fresh thyme • vegetable broth (1 liter) • heavy cream or almond cream for a vegan version (about 5 fl oz or 150 ml) • olive oil • Salt and pepper • hazelnut oil • curry powder • roasted hazelnuts, chopped, for serving (optional)