Peel and core the pears. Combine 2½ cups of the sugar and 5 cups water in a saucepan large enough to hold the pears. Split the vanilla beans the long way and scrape out the seeds; add both seeds and pods to the water. Turn the heat to medium-high and bring to a boil.
Add the pears and adjust the heat so that the mixture bubbles, but not too vigorously. Cook for