1. Peel the onions and thinly slice them. Peel the potatoes. If they're new potatoes or Jersey Royals, you can leave them unpeeled if you prefer. In which case just give them a scrub clean. Slice the potatoes as thinly as possible.
2. Pour 4 tbsp olive oil into a large ovenproof frying pan and warm over a medium-low heat (if you don’t have an ovenproof frying pan, see our tip below). Add the onions and potatoes along with a good pinch of salt and pepper. Gently fry the potatoes and onions for 20 mins, turning once or twice, till the potatoes are tender and golden at the edges.
3. While the potatoes are cooking, break the eggs into a bowl. Add a pinch of salt and pepper and whisk well.
4. When the potatoes and onions are tender, pour the egg mixture into the pan. Use a spoon to flatten the potatoes into an even layer, and turn the temperature under the pan down to very low. Cook for 15 mins till set. Make sure to keep the heat low, so it doesn’t catch and burn underneath. If it does, and you can’t turn the heat down further, you can transfer the omelette to the grill a little early to finish cooking it.
5. Preheat your grill to high. When the omelette has cooked on the hob for 15 mins, slide the pan under the grill. Grill for 3-4 mins, till the top is golden and set. Remove the pan from the grill and set aside to cool for a few mins.
6. Serve the omelette in slices. It's great as part of a tapas meal, or trying serving it alongside grilled padron peppers, a tomato salad and warm flat breads to make a hearty dinner.
7. Love Your Leftovers
If you have any omelette leftover, you can transfer it to an airtight tub and store in the fridge for up to 3 days. The omelette is best eaten cold.
8. The Right Pan For The Job
If your frying pan isn’t suitable for sliding under the grill, then transfer the cooked potatoes and onions to a snug heatproof dish before you add the beaten eggs. Pour over the beaten eggs and slide the dish under the grill to cook the frittata through (it will take a few more mins).