Penne Pasta With Celery Root Sauce

Ingredients

• 10 1/2 ounces dried large penne, pennoni, with ridges (rigate)
• 3/4 cup parmesan
• 2 tablespoons finely chopped fresh flat-leaf parsley
• Salt and pepper
• 4 tablespoons unsalted butter
• 1 onion
• 3 1/2 ounces cooked ham
• 1 1/3 pound celery root
• About 3 1/2 tablespoons milk
• You could use macaroni, sedani, elbows or rigatoni.