Did we find an authentic Palestinian Arab dish?

From Ma'an:

Prime Minister Salam Fayyad seen testing a massive dish of musakhan, a traditional Palestinian food, in the West Bank village of Arura, near Ramallah on 19 April 2010. The dish has a diameter of 4 meters.

Chefs are hoping to win an entry in the Guinness Book of World Records for the largest dish of musakhan ever made. It contained 500 chickens, 500 kg of onions, 250 kg of flour, 170 liters of olive oil, 70 kg of almonds and 50 kg of spices and sumac.

Is musakhan a Palestinian food?

It seems that this depends on your definition of "Palestinian." Mentions of the food in the media in the past decade or so generally call it Palestinian, but that was not always the case. In this fluff piece for the Saudi Aramco World magazine from 1975, it is identified as Jordanian:

Jordan’s Legendary Musakahan

To people with a desert heritage, the idea of cooking on or in earth, by the heat of the sun, a twig fire, or hot stones, is the natural way to a meal. From Aqaba to Baghdad, the bread baking in the ashes, tea bubbling on hot rocks, the bird roasting in a jacket of mud, this has been cookery through the millennia.

Not that that Dior-dressed lady over there is going home to fashionable Jabal Amman to poke up a fire among hot rocks. She may not even turn on her electric stove if she's having people in to dinner. She'll probably send out for that legendary Jordan Valley specialty, musakhan —literally "heated"—a succulent concoction of chicken, bread, onions and sumac baked in a tabboun.

The tabboun is the mud igloo once found in the back yard of old Jordanian homes. Its dome, over a mud-and-stone baking surface, over a fire trench, builds up and holds an intense, even heat which demonstrably adds a different flavor to baked bread, roasted meat. This venerable institution is sometimes found today even in cities, where neighborhoods have hung onto their ancient communal tabboun, the local bakery. After the baker has finished his day's allotment of loaves, the oven stays hot for hours, and in it will be found the dinners of his neighbors—a whole lamb at the back, a stuffed chicken, a casserole of eggplant.

So it appears that Musakhan originated in the Jordan Valley, which includes parts of British Mandate Palestine and parts of today's Jordan.

Palestinian Arabs are now claiming the food as pretty much exclusively their own (see Wikipedia's stub entry.)