1. Combine the sugar, water, lemon zest, and lemon juice in a non-aluminum 4-quart saucepan.
2. Add the vanilla seeds and bean to the saucepan.
3. Bring the mixture to a simmer over medium high heat and cook until the sugar dissolves.
4. Remove from the heat and set aside.
5. Peel the pears, leaving the stem intact.
6. Using a melon baller, scoop out the core of the pear from the bottom.
7. Place the pears in the poaching liquid and return them to the heat.
NOTE: To keep pears submerged, cut a circle of parchment paper just a little smaller than the diameter of the saucepan and place the circle over the pears.
8. Bring the pears to a gentle boil, then reduce the heat to a simmer.
9. Poach the pears until tender, about 30 minutes. A toothpick should easily slide through the pear.
10. When the pears are fully poached, cool them to room temperature
11. Pour the pears and poaching liquid into a clean container, cover, and refrigerate until serving. Pears may be refrigerated over night.
Assemble the Poires Belle Hélène
1. Place a scoop of ice cream in each bowl.
2. Place a poached pear on top or beside the ice cream and drizzle with warm chocolate sauce.
3. Garnish with Crème Chantilly.