Preheat oven to 350°F. Remove all the packaging and nets from the ham.
Wrap the ham in several layers of foil and place in a baking pan. Fill the baking dish with water.
Place ham in the oven to warm, 10 mins per pound (6-8 mins for a boneless ham).
In a saucepan, combine sugar, champagne and sorrel. Allow this to cook on medium-low heat until it becomes a light syrup about 20 mins.
Remove ham from oven, discard water and remove foil. Peel away the skin and carve off the desired amount of fat. Using a sharp knife, score the ham diagonally.
Pour the sorrel syrup over the ham (strain so you pour only the sauce on the ham, not the pods).
Increase oven temperature to 475°F - 500°F. Add the ham, occasionally basting until dark and caramelized.
Remove from the oven when it has reached the desired colour and allow it to rest before carving.
Serve remaining sauce on the side.