Duchess Potatoes & Celery Root

2 lbs potatoes, peeled, cut into 1" pieces
1 1/2 lbs celery root, peeled cut into chunks
2 cloves garlic
1/4 cup butter
1 cup half-and-half
2 Tbsp grated Parmesan cheese
1 1/4 tsp salt
1/4 tsp pepper
1 Tbsp chopped fresh parsley

Preheat oven to 375 F. In large pot, combine vegetables and garlic with enough wter to cover. Bring to a boil. Reduce heat to medium; boil until teder, 20 minutes. Drain.
In same pot, over medium, melt butter in half-n-half. Add potato mixture, cheese, salt & pepper; mash. Pipe or spoon into ungreased 1 1/2 qt baking dish.

Bake until browned, 20 minutes. If desired, broil 5 minutes for browner top. Sprinkle with parsley.

(Make ahead: Refrigerate, covered up to one day. Remove from fridge 30 minutes before baking.