Mashed Potatoes with garlic

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[...]

1/2 lb celery root , peeled and cut into 1-inch chunks 1 large baking potato , peeled and cut in half 1 garlic clove , peeled 2 tablespoons milk 1 tablespoon[...]