Melt butter in a large stock pot on medium high heat until it bubbles (or heat olive oil until it shimmers).
Sauté carrots and onions in butter until onions are translucent, 8-10 minutes. Add the salt and stir well.
Add the stock, bay leaf, and nutmeg to the pot. Bring to a boil and reduce to a simmer, then cook until carrots are tender, about 10-15 minutes.
Remove bay leaf, then puree the soup. You can do this with an immersion blender right in the pot, or let it cool and transfer to regular blender. Season to taste with salt and pepper and more nutmeg, if desired.
Notes
To increase the sweetness for picky eaters, try mixing in a tablespoon of honey.