Place the liver in a large bowl with the venison shoulder, bacon offcuts, onion, garlic an sage. Mix thoroughly, cover and refrigerate for 2–3 hours or overnight.
Set up your mincer fitted with the coarse plate (7–8mm/3∕8in). Pass the meat and liver mixture through the mincer and put it back into the bowl. Add the wine, breadcrumbs and pork back fat, and season with some salt and pepper. Mix well.
At this stage you can fry a little patty of the mixture, if you like, taste it and adjust the seasoning of the main mixture accordingly. Remember to compensate for the fact that this pâté will be served cold, which takes the edge off the seasoning.
Heat the oven to 120°C/235°F/gas mark 1⁄2–1. Line a 1-litre (35fl oz) terrine with cling film, leaving some overhang around the edges.
Line the terrine with the bacon, leaving enough overhang to envelop the meaty mixture. Spoon in the pâté mixture and level off, then fold over the overhanging bacon, then the cling film. Cover with foil, or, if using a traditional terrine dish, use the heavy lid.
Stand the terrine in a high-sided roasting tin and pour in enough hot water to come two-thirds up the sides of the terrine dish. Cook in the oven for 11⁄2–2 hours.
Check the core temperature of the pâté with a temperature probe; it should register no higher than 72°C/160°F. Remove the pâté from the oven and leave it to cool.
Place a suitably sized weight over the top of the pate (a similar sized terrine dish works well) and place it in the fridge to set firm, overnight if possible. Serve with toast, pickles and mustard or a sweet hedgerow jelly.