This is a simple dish. Quantities for my family, adjust for yours. As with all cooking -- this is art, not science, you can subsititute and vary amounts to your taste.

Fine dice (about 3/16" pieces) one and a quarter pounds of onions. Boil in a half pound of butter until nicely browned. Peel and cut to large (about 1.5") chunks four to five pounds of potatos. Boil in water until a fork penetrates easily. Drain and return to pot. Add the buttery onions. Add a teaspoon (I'm low sodium) of salt and a teaspoon of black pepper. Grate in 12 ounces of cheddar cheese. Mash together with enough milk (I never measure, just add some, mash, add a bit more, etc.) until you get the creamy texture you want. Mash/mix to a consistent color -- which would be difficult with a white cheddar or a jack.