Place the pears in the liquid; add enough water to cover the pears. The pears will float; keep them submerged by setting a lid smaller than the circumference of the stockpot on top of them. Bring the liquid back to a bare simmer.
Cook the pears until they can be easily pierced with the tip of a paring knife, about 20 to 30 minutes. Remove from heat. Cool pears, then store in their poaching liquid. (Pears can be kept refrigerated for up to 3 days.)
When ready to serve, remove the pears from the liquid. Pour the poaching liquid into a saucepan and boil until syrupy, 5 to 10 minutes. Pour over the pears. Serve with whipped cream, crème fraìche, or yogurt, if desired.