Preheat the oven to 275 degrees F.
Layer the vegetables and the meat into the Dutch oven in this order: carrots, lamb, potatoes, onions.
Using a small bowl, stir the curry powder into part of the coconut milk. Add more coconut milk and stir. If you want to make your sauce thick, stir in the arrowroot.
Pour the coconut milk mixture over the meat and vegetables. Use a little more coconut milk to get the last of the curry seasoning out of the bowl. Pour the second can of coconut milk evenly over the other ingredients.
Pour the tomatoes evenly over the dish, and sprinkle with salt.
Cover the Dutch oven with foil and seal tightly. Set the lid of the Dutch oven on top of the foil.
Place in the oven and roast for 6 hours (7 hours at high altitude).
After roasting, stir the curry and test for salt and spiciness. You can still add a little curry powder or cayenne (optional) if you want it spicier. Garnish with cilantro or offer it on the table. For the batch shown in these photos, I was serving it to someone who avoids cilantro, so we used parsley in the dish.
Serve as-is or over rice, with saag and chutney on the side. Garnish as desired.