Preheat oven to 200°C.
Butter and dust with flour 2 x 20cm sandwich tins. Line the bottom of each tin with a sheet of baking parchment.
Spread the ground almonds in a baking tray and toast them in the oven. Check them at 1 minute intervals, stirring them around so they brown evenly. They can burn very easily, so keep a close eye on them. Browning usually takes about 2-3 minutes.
Reduce the oven temperature to 180°C.
Place the egg whites in a large mixing bowl and whisk them until they are very stiff. Gradually whisk in the sugar, 1 tablespoon at a time. Continue whisking until the egg whites become very stiff again, and then add the vanilla extract and the vinegar.
Gently fold in the almonds and spoon the meringue into each baking tin, dividing it equally. Smooth over the tops and bake for about 15-20 minutes or until the meringue is firm.
Remove from the oven and leave to cool for 5 minutes in the tins. Turn the meringues out onto a wire rack and remove the disks of baking parchment.
Whilst the meringue is cooling, make the caramel sauce and chocolate ganache. Warm the shop-bought caramel or toffee sauce and stir in half the salt. Add the rest to taste.
To make the ganache, place the chocolate in a heatproof bowl over a pan of just simmering water and melt the chocolate with two tablespoons of water and the icing sugar. Stir until it is a thick, creamy consistency. Leave to cool.
Fold the cooled chocolate mixture into the whipped cream.
Choose the nicest meringue half for the top of the cake. Place the other one on a serving plate, drizzle over the rum and half the salted caramel sauce. Spread the chocolate cream all over. Pop the meringue into the fridge for an hour to allow the chocolate cream to set. Drizzle with more salted caramel and serve.