Combine sugar, water, lemon zest, lemon juice, and the whole vanilla bean in a medium-large pan. Bring everything up to a simmer, and simmer until the sugar has dissolved.
While the sugar syrup cooks, use a potato peeler to peel off the outer skin of the pears, but leave the stems intact. Slice off a thin disc at the base of each pear so they can sit flat.
With a paring knife, carefully cut around the core at the bottom of the pears and remove the core and seeds. The cores are soft and small, so you don’t need to cut very much out.
Place the pears into the hot syrup in the saucepan and cover with a piece of baking parchment, which needs to cover the liquid to make sure the pears are submerged.
Simmer the pears in the syrup for 20 minutes then remove from heat. Leave them in the warm syrup while your prepare the chocolate sauce.
To make the sauce, put the chocolate and cream in a microwave safe bowl and microwave in 20 second increments, stirring well in between intervals, until the chocolate is smooth and shiny.
Add the pear liqueur to the chocolate, one tablespoon at a time, stirring well after each.
To serve, drain the pears on paper towels and then serve them with the hot chocolate sauce, and vanilla ice cream or whipped cream.
