Heat oil in 9 inch omelette pan. Fry garlic until golden and discard. Add potato slices and cook over medium heat. Add onions after 5 minutes; cook until potatoes are tender. Lift and turn potatoes and onions as they cook.
In a large bowl, beat eggs with a fork or wire whisk until slightly foamy; add salt and pepper to taste.
Add potatoes and onions to eggs, draining with a slotted spoon before you add them. Return egg and potato mixture to same skillet, adding more oil if necessary so that eggs will not stick. Spread evenly and cook over medium heat, shaking pan.
When eggs leave sides of pan, invert a plate over the pan and flip omelette onto plate. Slide omelette back into pan to brown other side. Repeat this process one more time.
Serve hot or at room temperature on a round china or glass plate.