Peal the potatoes, wash them and cook in salted water in an open saucepan for 20 to 25 minutes.
Peal the apples, remove the core and cut into slices. Put them in a saucepan with a cup of water and the sugar. Leave to cook uncovered for 15 minutes.
Drain the potatoes and mash them. Add the apple and their cooking juice. Season with salt and pepper and whip all of this into an homogeneous mash.
Cut the bacon into strips and cook without any addition in the bottom of a non-stick saucepan.
Peal and thinly slice the onions and cook them in the bacon fat.
Mix the bacon and the onions into the mash and pour into a pre-heated serving dish.
Cook the sausages in the same non-stick saucepan. Place them on top of the mash and serve.