Preheat the oven to 350 F
In a large ovenproof pot over medium heat, melt the butter until it’s just starting to bubble. Add the onions and ½ teaspoon of the salt and cook, stirring occasionally, for about 10 minutes, until the onions start to become amber in color. Push them to the sides of the pot and raise the temperature to high. Put the chicken pieces in the middle of the pot and sprinkle with the remaining 1 teaspoon salt. Cook without stirring for about 5 minutes to let some of the pieces brown. Add the einkorn berries, flour and thyme leaves and stir everything until it’s well combined. Add the sherry and, as it heats, use a wooden spoon to scrape any bits off the bottom of the pot. Pour the broth over everything, stir to combine, and bring to a boil. If you have parchment paper, wet and crumple up a piece and set it directly on the food in the pot (or skip this detail). Cover the pot with the lid and transfer to the oven to bake for 1 hour.
Remove the pot from the oven and take off the lid. Discard the parchment paper and sprinkle the shredded cheese on top. Set the oven to broil and slide the pot under the broiler for about 5 minutes, until the top of the casserole has a golden-brown cheesy crust. Since all broilers are a bit different, check the casserole’s progress once or twice. Serve hot directly from the pot.
