There are many takes on it but a simple search will turn up 100's of recipes.
Personally I boil potatoes in their jackets and set aside.
While they are cooking pop some Black Mustard seeds in a good bit of oil add Green chilis slivered, toor dal, a pinch or two of tumeric cook until dal get toasted.
Add sliced onions cook until soft but not colored.
Add peeled and coarsely chopped potato and stir to combine.