Mashed Potatoes With Celery Root

Ingredients

• 3 lbs yukon gold potatoes, peeled and cut into 2-inch pieces
• 1 lb celery root, peeled and cut into 2-inch pieces
• 2 garlic cloves, sliced
• 1 cup light cream
• 6 tablespoons butter, at room temp
• 4 tablespoons butter (optional)
• 1 1/2 teaspoons salt
• 1/2 teaspoon pepper
• 1/2 cup chopped chives, fresh