Heat the oil in a large skillet over medium high heat.
Add the potatoes and onions to the skillet. Cook the potatoes until tender and crispy, approximately 5-6 minutes.
Drain the oil from the skillet and return to the heat.
Whisk the eggs in a large bowl with the salt and pepper.
Add the eggs to the skillet and, using a spatula, move the potatoes around so the egg can get into the nooks and crannies. Cook the omelette until it's just set around the edges but still a little wobbly in the center.
Carefully, Invert the omelette by placing a large platter on top of the skillet and turning the omelette onto the platter.
Slide the omelette back into the skillet and continue cooking until crispy and golden, an additional 3 minutes.
Serve the omelette with hot sauce, chopped parsley or red bell pepper, if desired.
You can make your Spanish omelette up to a day in advance. To reheat, place in a 350˚F oven for 10-15 minutes or until warmed through.You can also serve your Spanish Tortilla at room temperature.