1. Cut each grapefruit into 8 wedges. Carefully pull the thick skin off each of the wedges. You don’t need the fruit (it can be incorporated into a fruit salad or smoothie). So you now have 16 wedges (from 2 grapefruits). Cut each wedge in half again lengthwise so that you now have 32 slices. 
2. Fill a large bowl generously with water and bring to a boil over high heat. As soon as the water boils, add the pieces of grapefruit peel. Using a long spoon, gently press them under the surface of the water and blanch for 30 seconds.
3. Pour the peels into a strainer in the sink. Rinse them well under cold running water and repeat the whole procedure again. Start again with fresh water. The aim is to remove some of the bitterness.
4. After blanching twice, dump the peels on a clean tea towel and let them dry. It’s important to let the peels dry thoroughly to prevent the sugar syrup from crystallizing later.
5. Now we’re going to make the syrup. To do this, dissolve the Zùsto in the water and put it on medium to high heat. Let all this cook for 2 minutes until the Zùsto is completely dissolved. Bring to a boil again and add the peels. Cover it all with a baking sheet (circle cut out) and put a plate on top to make sure the peels stay well submerged. Let all this boil briskly for 60 to 90 minutes until the peels are translucent and there is about 100 ml of syrup left in the pan. This can take up to 1 ½ hours. Drain the peels and use tongs to scoop them out of the pan and onto a cake rack. You won’t need the rest of the syrup. Set the peels aside at room temperature and let them dry uncovered. Now let this dry for 24 hours.
6. Melt the callets au bain marie. Dip the peels (halfway) one by one by hand into the melted chocolate and place them onto the cake rack. Let the chocolate solidify around the peel.

Enjoy!