Heat olive oil in a large pot. Dice onion and add to hot oil. Saute for 3-4 minutes.
Cut cauliflower into florets and add to pot with salt, pepper, 1 teaspoon lemon zest, juice of half the lemon, and nutmeg. Cook until cauliflower is slightly browned; 4-5 minutes.
Add broth. Once it boils, turn down heat to simmer for 10-15 minutes.
Using an immersion blender, blend until smooth. (You may also add a small amount to a high-powered blender and then add back to the pot to heat through).
Serve warm with bread slices and berries.