Preheat oven to 400 degrees. Heat butter in a large skillet. Add onion, carrots, celery and potatoes and sauté until carrots are just starting to soften. Remove vegetables and keep warm. Add duck halves, skin side down, and cook until skin is golden brown and crispy. Flip and cook for 2 to 3 minutes more. Arrange duck, breast side up, in a baking dish and top with the reserved vegetables. Before placing the dish in the oven (and away from any open flame), top with parsley and drizzle whiskey over duck.