Melt 4 tablespoons of butter in a large pot over medium heat. When hot, whisk in the flour, stirring constantly until it turns a pale golden brown, about 2-3 minutes. Slowly whisk in 6 cups of the vegetable broth, stirring constantly. Bring to a boil and add the carrots, leeks, chickpeas, salt, and thyme. Cook, stirring occasionally, for 10 minutes. If the liquid is looking a little low, add another cup or two of the vegetable broth, stirring to combine.
Meanwhile, prepare the dumplings: in a medium bowl, whisk together the flour, baking powder, and salt. Whisk together the buttermilk and egg together in a small bowl, then fold into the dry ingredients along with the 2 tablespoons of melted butter. Stir just to combine.
Using a small spoon or an ice cream scoop, dollop half tablespoon-sized balls of dough into the broth. Cover the pot and reduce heat to low. Cook until the dumplings have puffed up and are completely cooked through, about 20 minutes. (To test, take out a dumpling and cut it in half. It should no longer appear doughy.) Remove the lid and serve, garnished with fresh parsley.
Be careful when dropping the dumplings in the soup, they might splash! It might be easier if you lower them into the hot liquid on a spoon and let them slide off.
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