Preheat the oven to 200°C (400°F/gas mark 6).
Melt the butter in a sauté pan set over a medium heat, then add the onion and sauté for about 5 minutes, until softened. Remove the pan from the heat and mix in the sausagemeat, breadcrumbs, dried cranberries and herbs, then season generously.
Shape into a large roll, then wrap in a layer of parchment paper and tin foil, twisting the ends securely to seal. Cook in the oven for about 45 minutes, until cooked through and tender. Unwrap just before cutting into slices to serve.