Place the pearl onions into a medium-sized stockpot and add enough chicken stock to cover. Boil until tender, 8-10 minutes.
Drain, saving 3/4 cup of the chicken stock to use later in the sauce.
In a medium saucepan, melt the butter. Stir in the flour, salt and pepper until smooth. Cook, stirring, for 2-3 minutes until the flour has browned and starts to smell nutty.
Gradually whisk in the cream, then add the reserved broth, whisking to keep the sauce smooth.
Bring to a boil; cook and stir for 2 minutes or until the sauce starts to thicken.
Add in 1/2 to 1 cup of the cooked onions, then take an immersion blender and quickly puree until smooth.
Add in the rest of the onions and cook, on medium heat, until they are heated through.
Stir in the nutmeg, season again with salt and pepper if desired, then place in a bowl and garnish with fresh parsley to serve.
Notes
Pureeing the onions into the sauce not only thickens it, but also adds extra onion flavor to amp up the cream sauce!
Try a sprinkle of paprika on top if you're not a nutmeg fan