Melt the butter in a large saucepan over medium-high heat.
Add the onion and sauté for 2 minutes.
Mix in the carrots, cumin, coriander, cinnamon and allspice, and sauté for about 6-8 minutes, until the vegetables start to soften and the spices become fragrant.
Add the lentils, harissa and broth.
Bring the mixture to a boil, then reduce the heat to low and simmer until the carrots and the lentils are cooked through, about 20 minutes.
Remove the soup from the heat and purée with an immersion blender or in a blender, until smooth.
Return the puréed soup to the pot and stir in the maple syrup, lemon juice and season with salt and pepper to taste.
Reheat the soup over medium-low heat, if needed.
To serve, ladle the soup into pre-warmed bowls, and garnish with a swirl of yogurt, and a sprinkle of smoked paprika, ground cumin and a flurry of fresh chopped cilantro.
Serve with warmed naan bread or Moroccan khboz.
