Peel and core the apple and cut into fine cubes. Cut the onion and also cut into fine cubes. Fry both together with the oil and rosemary in a saucepan until it starts to smell, add the currants and let simmer for about 5 minutes and stir well.
Pull off the stove and let it get cold and mix everything together well in a blender, add the salt and the preserving sugar and season to taste again.
Bring to the boil, simmer for about 3 minutes and immediately pour hot into sterilized jars, close and turn upside down.
When the glasses are cold, turn them over again.
Use with: meat, poultry and as a dip, with grilled and fried food!