Crack six eggs into large mixing bowl, beat lightly with fork.
Heat 2.5 oz. olive oil in 9-inch skillet over medium-high heat, until oil begins to shimmer, about 2 minutes. Add potatoes. Cook and stir until tender, about 8 minutes. Add onion and salt, stir ensuring onions have an even coating of oil. Cook for about 6 more minutes, until potatoes are done. Remove from heat. Using a slotted spoon, add vegetables to mixing bowl containing eggs. Wipe out skillet to remove extra bits clinging to surface.
Fold vegetables into eggs until blended, about 1 minute. Add remaining oil to skillet. Reheat and pour contents of mixing bowl into skillet. Shake once or twice to ensure mix is evenly distributed. Cook until edges begin to brown and eggs become firm. Run sharp knife around the side of skillet to release omlette from skillet.
Cover skillet with plate and flip contents onto plate. Slide omlette back onto skillet and cook until done, about two minutes. Remove from heat and serve tableside.