Tie the herbs in cheesecloth to make a small bundle if using.
Peel the parsley root. If they're very clean they can simply be scrubbed.
Thinly slice the parsley root into ½ inch rounds.
Put the parsley root and cream in a sauce pot about 8 inches wide. Cover with a circle of parchment paper. Bring the pot to a simmer over medium heat.
Put the herb bundle in the bottom of the pot if using to help it infuse into the cream.
Cook for 15-20 minutes until the roots are very tender. Stir the pot occasionally, until most of the liquid is absorbed. Discard the herb bouquet, pressing any liquid back onto the roots.
Transfer the parsley roots to a highspeed blender or food processor, add the butter and puree until smooth. Double check the seasoning for salt and adjust until it tastes good to you.
The puree will keep in the fridge for 4-5 days. You can keep it in a warm oven covered with parchment or a lid before serving.
Serve the puree as a dollop on a plate as you would a small serving of mashed potatoes. It's fantastic with scallops and fish, as well as poultry.
Video
Notes
The puree can be served as-is, or used to flavor mashed potatoes. It's thick and can splatter on a stove so I like to hold it warm in a small sauce pot covered with parchment.