Heat 1 tablespoon of olive oil in a large nonstick skillet over moderate heat.

Add the sliced onion, rosemary, thyme, salt, and pepper to the skillet.

Cook, stirring occasionally, until the onion is golden, about 5-7 minutes.

Remove from heat and let the onion mixture cool slightly.

In a bowl, whisk together the whole eggs, egg whites, salt, and pepper.

Add the cooled onion mixture to the egg mixture and stir to combine.

Heat 1 tablespoon of olive oil in the same skillet over moderate heat.

Pour the egg mixture into the skillet and cook until the edges begin to set, about 3 minutes.

Add the sliced potatoes, spreading them in an even layer over the egg mixture.

Reduce the heat to moderately low, cover the skillet, and cook until the eggs are almost completely set, about 6-8 minutes.

Place a plate over the skillet and invert the omelette onto the plate.

Add the remaining 1 tablespoon of olive oil to the skillet and turn the pan to coat the bottom with oil.

Slip the omelette back into the skillet.

Cook for 3 minutes more, or until the bottom is just set.

Transfer the omelette to a serving dish.

Cut into wedges and serve hot or warm.