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Peel and rinse the potatoes and chop them into pieces. The bigger the pieces are, the longer it takes to cook them. Add the potatoes to the medium-sized pan and fill the pan with water and season with salt.
Boil the potatoes for about 10 minutes, depending on their size. Meanwhile rinse the fresh escarole, dry it using the salad spinner and chop them into small pieces.
Set the rinsed and chopped escarole aside and peel the onion. Slice the onion into small chunks and set aside.
Heat up the medium-sized skillet and saute the bacon lardons without adding any extra oil or butter. Add the chopped onion after about 2 minutes and saute for a few minutes more. (the bacon needs to be crunchy)
Drain the potatoes and mash them, you can use a potato masher or a fine sieve and a ladle to do this. The potatoes don't need to be super smooth, but there shouldn't be any big lumps left.
Stir in the chopped raw escarole and bacon with its fat and onion. Add milk and vinegar, maybe you'll need a bit more milk to create a smoother mash. Season with pepper and salt, enjoy your meal!