To make the sausages: place all the ingredients in a medium-sized bowl and using clean hands, mix and knead together until sticky and combined well. Shape the mixture into 8 even-sized sausages, put on a plate and cover and refrigerate for at least 1 hour or overnight.
To prepare the onion gravy: heat the oil and butter together in a large frying pan over low-medium heat. Cook the onion until softened and golden. Add the flour to the pan and cook, stirring with a wooden spoon, for 20 seconds. Pour in the wine and stock, stirring to prevent lumps, and bring to a boil. Reduce the heat and gently simmer for a few minutes, or until thick enough to coat the back of the spoon. Keep warm until needed.
To make the mash: Preheat the oven to 350 degrees F (180 C).
Place the whole garlic bulb on a piece of foil and drizzle with oil. Wrap with the foil and place on a baking sheet. Roast in the oven for 30 to 40 minutes, until very soft. Set aside to cool slightly.
Peel and halve (or quarter) the potatoes and place in a large saucepan of cold salted water. Cover and bring to a boil over high heat. Uncover and boil for 15 minutes, or until tender when tested with a skewer or fork. Drain. Use a food mill or potato ricer to puree the potato and return it to the pan.
Heat the cream (or milk) and butter together in a small saucepan over medium heat, until the butter has melted and the cream is hot. Pour into the potato and using a wooden spoon, beat to combine.
Cut the base off the roasted garlic bulb and squeeze out the softened cloves starting from the tip and pressing down. Add to the potato and beat to combine. Season with salt and pepper and serve.
To finish: Heat the oil in a large frying pan over medium heat and cook the sausages for 10 minutes, turning occasionally, until brown all over (I cooked mine longer to make sure it would cook through–alternatively, it wouldn’t be a bad idea to finish them off in the oven if you are worried about them cooking through).
Serve the sausages with potato mash and onion gravy.