Barbecued Butterflied Leg of Lamb with Mint

Lay meat boned side up.
Slash about halfway through thickest portions, as needed, and pull meat, patting cut edges down, to make the piece relatively even.
Place lamb in a 9x13 inch pan.
In a 1 1/2 quart pan over medium-high heat, stir vinegar with 13 cup mint jelly just until boiling.
Stir in mint and pour evenly over lamb.
Cover and chill 2 hours or up to a day.
Turn meat over occasionally.
On firegrate in a barbecue, with a lid, ignite 50 to 60 charcoal briquets.
When briquets are dotted with ash, in about 30 minutes, spread them into a single layer; scatter 10 to 12 more briquets over coals.
Set grill 5 to 6 inch above coals.
Lift meat onto grill; reserve marinade.
Put lid on barbecue and open vents.
Turn meat as needed to brown evenly; baste with marinade.
Cook until thickest part of meat is done to your liking; for rare (140' on a thermometer) in center of thickest part, allow about 40 minutes total.
Thinner sections will be well done.
Transfer lamb to a platter and let rest 5 to 10 minutes.
Garnish with mint sprigs.
Slice meat thin.
Season to taste with mint jelly, salt, and pepper.
Eat with knife and fork or tuck into pocket bread.