Peel the turnips and carrots and cut into cubes. Put together in a pressure cooker with the stock. Poke the cooked sausages and add them together with the streaky bacon. Cook with the lid closed for about 15-20 minutes.
Peel and quarter the potatoes. Cook in salted water for 20 minutes.
Remove the sausage and bacon from the pressure cooker, use a ladle to skim off the broth and set aside. Drain the potatoes and place in the pressure cooker. Crush everything with a pounder and add the stock until the desired degree of mousse is achieved.
Serve the puree with the cooked sausages and, if you like, the bacon.