Heat a small saucepan over a moderate heat until hot. Carefully pour in the balsamic vinegar and sugar, whisking all the time as you bring the vinegar to the boil. Continue boiling and whisking until the vinegar has reduced by half and you have a thin syrup consistency.
Remove from the heat and set to one side. Arrange the sliced red onion on the base of a serving platter. Top with the halved strawberries, then tear the basil leaves and scatter all over.
Sprinkle the feta on top and season. Finish the salad by drizzling the balsamic reduction all over the salad. Serve immediately.
See more Salad recipes