Melt the butter in a 4-quart heavy saucepan over medium heat and cook the shallot, stirring, until translucent, about 4 minutes. Add the squash, coriander, cumin, 1/2 teaspoon each salt and pepper. Stir until coated. Pour in the broth and bring to a simmer and cook, uncovered, until the squash is very tender, 25 to 30 minutes.
Carefully puree the soup with an immersion blender or in a stand blender, in batches, until very smooth. Return the soup to the saucepan and stir in the cream. Season salt and pepper. Reheat the soup before serving if necessary.
For the herb oil and harissa:
Bring a small saucepan of water to a boil. Add the parsley and cook, uncovered, until bright green, 30 to 45 seconds. Transfer with a slotted spoon to a bowl of ice water and then drain and pat dry. Puree in a blender with the grapeseed oil until the oil is bright green, about 1 minute. Strain the parsley oil through a fine-mesh sieve. Do not press on the solids. Whisk the harissa and 1 tablespoon water together in a small bowl until smooth.
For the crab salad:
Whisk the oil, lemon juice, ginger, 1 teaspoon salt and 1/2 teaspoon pepper together in a medium bowl. Add the crab, cilantro and mint and gently toss to combine.
Divide the hot soup evenly among 4 serving bowls and mound some crab salad in the middle of each bowl. Drizzle each bowl with parsley oil and harissa.
Harissa is a North African condiment made from spices and chilies. It can be found in specialty food markets.