Tortilla Española with Saffron Aioli

Ingredients

• 700g Maris Piper or other waxy-ish potatoes, peeled
• 1 large brown onion
• 400ml mild olive oil (for confit-cooking — most gets strained back)
• 1 tsp fine sea salt
• 8 large eggs
• ½ tsp fine sea salt
• black pepper
• generous pinch saffron threads (about 20 strands)
• 1 tbsp just-boiled water
• 150g good-quality mayonnaise
• 2 tbsp garlic-infused olive oil
• 1 tsp lemon juice, plus more to taste
• pinch of sea salt

Method

1. Slice the peeled potatoes into rough 3-4mm coins — irregular is fine, you want some to break down and some to hold shape, that's what gives a proper tortilla its custardy interior. Halve the onion and slice thinly.
2. Pour the olive oil into a 24cm non-stick frying pan and warm over a medium-low heat. Add the potatoes and onion — the oil should just cover them and barely bubble, not sizzle. This is a confit, not a fry. If it's spitting hard, drop the heat. Season with the teaspoon of salt.
3. Cook gently for 25-30 minutes, stirring every 5 minutes or so with a slotted spoon. The potatoes are done when a slice crushes easily against the side of the pan with the back of the spoon — soft, surrendering, but not coloured. If they're going golden you're cooking too hot; pull the heat down. Drain through a sieve set over a bowl, reserving the oil.
4. Make the saffron aioli while the potatoes drain. Crumble the saffron between your fingers into a small bowl and pour over the just-boiled water. Leave for 5 minutes — you want a deep orange-red infusion, not pale yellow. Whisk in the mayonnaise, garlic oil, lemon juice and salt. Taste and adjust. Cover and chill.
5. Crack the eggs into a large bowl, add the half-teaspoon of salt and a good grind of pepper, and beat until just combined — no need to froth. Tip the warm drained potatoes and onion straight into the eggs and fold gently. Let it sit for 5 minutes; the warm potatoes start cooking the eggs from within and the starch thickens the mix, which is what gives tortilla its proper set.
6. Wipe the pan clean and return 2 tablespoons of the reserved confit oil to it. Heat over a medium-high heat until the oil shimmers — you need it properly hot or the tortilla will stick on the flip. Pour in the egg and potato mixture and immediately drop the heat to medium-low. Use a spatula to push the edges in toward the centre for the first minute, the way you would a French omelette, building a soft border.
7. Cook undisturbed for 6-8 minutes. The edges should be set and lifting slightly from the pan, the top still wet and wobbly in the middle. Run the spatula around the rim and underneath to make sure nothing is stuck — this is the moment people fail the flip, so check properly.
8. The flip. Place a flat plate larger than the pan over the top. Hold the plate firmly against the pan with one hand, lift with the other, and in one confident motion invert — don't hesitate halfway, that's how it splits. Set the pan back on the heat, add a splash more of the reserved oil, and slide the tortilla back in cooked-side up. Tuck the edges under with the spatula to round it off.
9. Cook for another 3-4 minutes for a properly Spanish jugoso (juicy) centre — press the top gently and it should feel set at the edges but with a slight give in the middle, like a firm sponge. If you want it fully set through, give it 5-6 minutes. Slide onto a clean plate.
10. Rest at room temperature for at least 20 minutes before slicing — tortilla is never served hot in Spain. The eggs continue to set as it cools and the flavour opens up. Cut into wedges or 3cm cubes for picnic squares, and serve with the saffron aioli alongside.