Preheat oven to 350°F. Break the garlic head apart and place the cloves in a piece of parchment paper. Wrap in foil and bake for 20 minutes. Flip the packet and bake another 5–10 minutes until soft. Set aside.
Place the parsnips in a pot and cover with cold water. Add a pinch of salt, bring to a boil, then reduce to a simmer and cook until very tender, about 15–20 minutes.
Drain the parsnips very well, then return them to the hot pot and let them sit uncovered for 1–2 minutes so excess steam can evaporate. This step helps prevent a watery mash.
Squeeze the roasted garlic cloves out of their skins and add them to the parsnips. Mash by hand or puree with an immersion blender or food processor.
Stir in the cashew cream. If needed, add plant milk a little at a time until the desired consistency is reached. Keep the mash thick rather than loose.
Season with salt and freshly ground black pepper to taste. Add a small pinch of white pepper or nutmeg if desired. Serve warm.