In a large stockpot, heat the oil over medium heat. Add the onion and sauté until it beings to turn golden brown, 4 to 5 minutes.
Add the garlic, coriander, cardamom, pepper and bay leaf and stir for 30 seconds. Add the fennel and ½ cup of the broth and cook, uncovered, stirring frequently, for 7 minutes.
Add the pears and the remaining 3½ cups broth. Cover, raise the heat, and bring to a boil. Lower the heat and simmer until the fennel is soft and tender, 35 to 40 minutes. Uncover, let cool, and remove the bay leaf.
In batches, transfer the soup to a blender and puree until smooth. Return the soup to the pot and keep warm until serving.
Portion into serving bowls and garnish each bowl with a drizzle of oil (if desired), fennel fronds and salt, to taste.