To make the sumac rub, combine all ingredients and pulse in a spice or coffee grinder. Store in a mason jar or airtight container and keep in the pantry for up to one month. This recipe will yield 1¾ cups.
Preheat oven to 400 degrees. Remove leg of lamb from refrigerator; rub with Jordan extra virgin olive oil, lemon juice and ½ cup of the Jordan Sumac Rub. Allow lamb to come to room temperature.
Place lamb on a rack in a shallow pan and roast for 30 minutes. Reduce oven to 325 degrees and roast until a meat thermometer reads 135 degrees (approximately one hour and forty five minutes).
Remove lamb from oven and allow to rest, tented with foil for 15 minutes. Accompany with a simple Greek salad, grilled eggplant, pita and tzatziki for a rustic meal.