In a large pot over medium heat, melt the ghee. Add the onions, garlic, carrots and potato. Cook, stirring until starting to soften, about 7 min.Add the lentils, tomatoes & spices. Cook for 1-2 minutes until fragrant.Add the stock, bring to the boil then turn down the heat to low and simmer for 35-45 min, until vegetables are very soft (test a carrot, if it is soft, then all the rest will be too).While the soup is simmering, make the croutons: Preheat oven to 200 C. Use scissors or a knife to cut up the pita bread into small squares, or just tear roughly with your hands into bite-sized pieces. Toss with a generous drizzle of olive oil and sprinkle with a little salt then spread on a baking sheet in a single layer. Place in oven for about 10-12 minutes, until golden and crispy.Puree the soup with a stick blender (also known as an immersion blender), or in a regular blender in batches, until completely smooth. (TIP: if you make lots of soup, I highly recommend buying a stick blender. They are quite cheap and save SO much time and cleaning up!)Adjust seasoning and serve with croutons and a sprinkle of dukkah if you like.