Preheat the oven to 320°F/160°C.
Combine salt, pepper, cumin, date syrup, mustard, and olive oil to make the sauce.
Arrange the onions, sweet potatoes, chestnuts, and short ribs in a baking dish.
Pour the sauce, water, and thyme evenly over the ingredients. Cover with parchment paper and then aluminum foil.
Bake for 3 to 3.5 hours, until the meat is tender.
Remove the cover and bake for an additional 20 to 30 minutes to brown the top. Serve warm.