Cook the venison stock, filter and put to one side.
Prepare the polenta in the traditional manner with the addition of the butter, and when ready, spread in a gastronorm baking tray lined with lightly oiled baking parchment.
Dilute the ragout a little and pour a layer about cm thick over the polenta.
When the polenta has cooled to body heat (it will feel tepid when touched), roll it up evenly and carefully.
Put it in the fridge to firm up.