Peel the pears and core with a corer or a small paring knife, being sure to remove the tart center core area of each. Place the sugar, green tea, gingerroot, lemon peel and mint in a medium size saucepan large enough to hold the four pears in a single layer.
Over medium heat, bring the mixture to just under a boil, or until the sugar is fully dissolved. Reduce heat to a simmer and add the peeled and cored pears. Cook for about 15 to 20 minutes. The pears will remain firm. Cool to room temperature and then refrigerate, covered. Meanwhile, make the Pistachio Cream Sauce.
Pistachio Cream Sauce: In a small bowl, whisk together the yogurt, buttermilk and maple syrup. Add nuts and store mixture in refrigerator until your guests are ready to eat.
Assembly: Remove pears from poaching liquid, drain well and place one each in four chilled goblets. Mask with the sauce and serve immediately, garnished with fresh mint leaves, if desired.