Potato Stuffing Casserole

From Taste of Home.

1/4 C. chopped celery
1 onion, chopped
4 Tbsp. butter, divided
3 slices bread, cubed
4 to 5 large potatoes, peeled, cooked, and mashed
1/4 C. chopped fresh parsley
1/2 tsp. salt
1/4 tsp. pepper
1 C. hot whole milk
1 large egg, beaten

In a medium skillet, saute celery and onion in 2 tablespoons of butter until tender. Add bread cubes and stir until lightly browned. Stir in potatoes, parsley, salt, pepper, milk, and egg; mix well.

Spoon into a greased 1-1/2-quart baking dish. Dot with remaining butter. Bake at 350 degrees, uncovered, for 30-40 minutes or until lightly browned.