For the parsnip purée, peel the parsnips, cut out the core and cut into smallish chunks. Peel the potatoes and cut into smallish chunks.
Heat the butter and oil in a frying pan. Add the potatoes and parsnips and fry for about five minutes.
Pour in the chicken stock and simmer until the vegetables are tender.
Add the double cream and cook until almost completely reduced.
Remove from the heat and leave to cool for a few minutes. Using a hand-blender, blend the vegetables to a purée, before passing through a sieve into a clean pan.
Season to taste with salt and freshly ground black pepper.
