Add the potatoes to the pot, season with salt, and bring to a boil over high heat. Lower to a simmer and cook the potatoes and parsnips until tender but
not falling apart. Drain and transfer back into the pot or a large bowl.
Begin to mash the hot potatoes. Add in the butter, heavy cream (add more if needed), garlic, and season with salt and pepper to taste. Fold in the parsley.
Serve right away.