Separate the chicory into individual leaves, removing the stem in a wedge shape.
Remove the peel from the orange so that the white skin is completely removed. Cut the fillets from the partitions, collecting the juice. Squeeze the rest of the orange: you should have a total of 2-3 tbsp of orange juice. Remove the skin from the apple, cut it into quarters and cut out the core. Cut the quarters into small cubes.
For the vinaigrette, whisk together the white wine vinegar, the collected orange juice and the sour cream, then add the oil. Season with salt, pepper and sugar. Add the apple cubes to the sauce form.
Divide the chicory leaves evenly on serving plates, spoon the sauce with the apple pieces over them. Garnish with orange fillets.