Peel the parsnips, cut them into large chunks then bring them to the boil in a pan of deep, salted water. Do the same with the carrots, but peeling them only if they have thick skins. Turn the heat down to a lively simmer then leave to cook for about 20 minutes until they are soft enough to mash.
Toast the pine kernels until golden in a dry pan then set aside. Finely chop the parsley. When the parsnips are tender, drain them, add half the butter, then mash until creamy, using a stick blender, food mixer or vegetable masher.
Drain the carrots, add the remaining butter then mash until smooth and creamy. Fold in the chopped parsley. Put the two mashes into a warm serving dish, then fold the two together, gently, so they are lightly mixed. Scatter with the toasted pine kernels.