1. Preheat the oven to 140°C, fan oven 120°C, Gas Mark 1. Draw a 30cm diameter circle on a sheet of non-stick baking parchment. Place a couple of drops of oil onto a baking sheet, and put the baking paper on top (the oil will help to prevent it from moving).
2. Put the egg whites into a large grease-free bowl. Using a hand-held electric whisk with scrupulously clean beaters, whisk the egg whites on full speed until they hold their shape. Gradually add the Caster sugar, whisking well on high speed until the egg whites are very stiff and glossy.
3. Fold the chia seeds through the mixture. Heap half the meringue onto the baking paper and spread it out with a palette knife or the back of a spoon into an even layer over the circle. Heap the remaining meringue around the outside edge to form a border.
4. Transfer to the middle shelf of the oven and bake for 1½-2 hours. The meringue will dry out rather than cook at this low temperature. It won’t harm the meringue if you open the door at any time. Cool the meringue completely, then carefully remove the lining paper. Transfer to a serving plate.
5. Whip the cream in a large chilled bowl until it holds its shape. Fold through the lime zest, then spoon it on top of the meringue and spread it out to cover the centre up to the border. Spoon the blueberry jam and remaining blueberries on top. Serve, decorated with lime slices and mint sprigs.
