Heat the oven to 200C, 180C fan, gas 6. Line 3 baking sheets with baking parchment and mark each with a 20cm circle.
Top the cherry compote into a wide sieve over a bowl and stir gently. Leave to drain for 20 minutes.
Whisk the egg whites in a large, clean mixing bowl using an electric mixer until stiff peaks form. Gradually add the caster sugar, 1 tbsp at a time, whisking well after each addition, bringing the whites back to stiff peaks before you add more sugar.
Once you've whisked in half the sugar, add the rest in larger quantities. When all the sugar has been added, whisk the meringue back to glossy, stiff peaks, then whisk in the vinegar and cornflour.
Divide half the meringue between two of the circles, leaving a 2cm gap at the edge to allow for spreading. Use a palette knife to level off a little.
Spoon the remaining meringue mixture into the third circle and use the back of a metal spoon to make pillowy swirls at the edge.
Put the meringue in the oven and immediately reduce the temperature to 130C, 110C fan oven, gas ¾. Bake for 2 hours, then switch the meringues around on the shelves and turn off the oven. Leave the meringues inside to cool overnight. Remove, carefully peel off the baking paper and set aside.
Meanwhile, put the drained cherry compote liquid in a small saucepan with half the liqueur or orange juice. Bring to the boil then bubble gently until reduced by half. Leave to cool. Stir the remaining liqueur into the drained cherries.
Put the chocolate pieces in a heatproof bowl. Bring the cream to the boil in a small saucepan or the microwave and pour over the chocolate. Stir until the chocolate has melted and the mixture is smooth. Chill.
Whisk the chilled chocolate mixture with an electric whisk until the consistency of whipped cream. Whisk in half the chilled cherry liquid, which will be lightly thickened.
To assemble the meringue, put one of the rounds on a serving plate. Spoon half the chocolate ganache onto the meringue and gently smooth to the edges. Spoon on half the drained cherries and a drizzle of the remaining thickened juices.
Add a second round of meringue, flat side up, and dollop on the all but 2-3 tablespoons of the ganache, the remaining cherries and juices. Top with the thicker pillowy meringue.
Spoon the remaining ganache into the centre at the top, scatter with fresh cherries and chocolate curls. Chill in the fridge for 1-2 hours before serving to allow the meringue to soften a little.
The assembled meringue, minus the fresh cherries will freeze for up to 2 weeks. Defrost overnight in the fridge.
Crème de Cassis is also delicious in the cherry juices as an alternative to Cointreau.