This puree garnish looks great and tastes very interesting.
It can be served as a vegetarian menu or complement steaks with different sauces.
If you cannot find blue potatoes you can substitute them with sweet potatoes, carrots or peas.
Boil the 2 types of potatoes separately.
From the classic potatoes make a puree (with sour cream, some butter and salt or soy cream - for a vegetarian pure preparation).
Chop the blue potatoes into cubes and mix with the puree.
Serve hot with salad or pickles.
Enjoy your meal!