Put the berries (except the reserved ones) in a blender or food processor and whizz together to make a purée. Pass the purée through a fine sieve to remove the pips.
Place 1/2 cup of caster sugar in a small saucepan with 1 1/2 tablespoons of water. Dissolve over a medium-low heat; don't stir once the mixture comes to the boil. Slowly continue heating until it caramelises and looks a rich golden colour. Immediately remove the pan from the heat.
Carefully add the blackcurrant cordial, lemon juice and fruit purée. Stir until the caramel is incorporated, then leave the coulis to cool.
Add a pinch of salt to the egg whites in a clean bowl and whisk into stiff peaks. Sprinkle with the remaining tablespoon of sugar and continue whisking until the meringue is glossy.
Fill a deep frying pan two-thirds full with water and heat to just below the boiling point. Using a tablespoon, float six dollops of the meringue mixture on the water. Cook gently for 30 seconds, then turn over using a slotted spoon and cook for 30 seconds on the other side. Remove from the pan with a slotted spoon, place on a clean cloth and leave to cool.
When ready to serve, pour the coulis into individual dishes and float a meringue on each. Garnish with the reserved strawberries.