Warm the olive oil in a large pot over medium heat. Add the onion and cook for about 5 minutes until softened. Stir in the garlic for 30 seconds.
Add the squash, broth, salt, pepper, and nutmeg. Bring to a boil, then reduce to a gentle simmer. Cover and cook for 20 to 25 minutes, until the squash is fork-tender.
Turn off the heat and puree until completely smooth with an immersion blender. If using a countertop blender, work in small batches and vent the lid carefully because hot liquid expands.
Stir in the half-and-half and warm gently without boiling. Taste and adjust the seasoning. Serve hot with toasted pepitas.