Peel and Boil potatoes until they are cooked but not mashable. (they will finish cooking in the oven later) -- Let cool and slice thin (1/2" slices are great!)
Slice onions to thin strips (not dice) - Chop garlic
In a hot skillet with olive oil, sautee onions until starting to caramelize, then add garlic (garlic will burn if added too soon). Let cool when finished.
While this is happening, grate cheese.
In a casserole dish, spray with PAM or other spray fat. This will make clean up a breeze!
Start layering potatoes, onions, and cheese. repeat. and repeat. When you're out of potatoes, put the rest of cheese (maybe grate some more! I'm a cheeze hound)... Cover and bake in 375 degree preheated oven for 1.5 hours. Take lid off dish 10-20 minutes before finishing to give it a nice golden crust (my favorite part)