Heat the butter and oil in a large saucepan until butter melts. Add the carrots, onion, celery, salt sugar and coriander. Stir the vegetables around and cook until they begin to release liquid and become softened, about 5 minutes.
Pour in 6 cups water or vegetable stock and bring to a simmer. Cook about 15 minutes, or until the carrots are tender. Remove from the heat and cool for a bit, then puree the soup in a blender until completely smooth. Stir in lemon juice and taste for salt.
To make the pesto
Reserve a few parsley leaves for the garnish and chop the rest in a small food processor until finely chopped. Add all but 1 tablespoon of the almonds and pulse until the nuts are finely chopped and the mixture forms a paste. Add the fennel seeds, olive oil, salt to taste and the cheese and pulse to combine.
Serve the soup with a spoonful of pesto and sprinkle with remaining parsley leaves and almonds.
Use any leftover pesto within a day or two, tossed with roasted vegetables or spread on a warm crostini.
To make this vegan, substitute the butter with coconut oil or use all olive oil.