Preheat the oven gas 1, 140°C, fan 120°C. Place 4 room-temperature egg whites into a large, clean, grease-free bowl.
Using an electric whisk, start whisking at a low speed, increasing it as the whites froth up and swell in volume.
Once the whites are nice and stiff, gradually add 225g (7 1/2oz) caster sugar, a couple of tablespoons at a time.
Continue whisking until the mixture is firm and moussey, with a glossy sheen. Then line two baking sheets with nonstick baking paper.
Place spoonfuls of the mixture onto the trays, leaving space between each one. Bake for 40-45 mins, until the meringues are crisp on the outside.
Turn off the oven, leaving them inside to cook for about 30-40 more minutes (for a crisp outside and a soft inside). Once cool, take them off the paper.