Cut the bacon into 1in/ 3cm squares. Bring the stock to the boil in a medium saucepan which has a well-fitting lid, add the sausages and the bacon and simmer for about 5 minutes. Remove the sausages and bacon and save the liquid. Cut each sausage into four or five pieces. Peel the potatoes and cut into thick slices. Skin the onions and slice them. Assemble a layer of potatoes in the saucepan, followed by a layer of onions and then half the sausages and bacon. Repeat the process once more and then finish off with a layer of potatoes. Pour the reserved stock over and season lightly to taste. Cover and simmer gently for about an hour. Adjust the seasoning and serve piping hot.