Place the first 5 ingredients in a medium pot. Set over medium-high heat, bring to a boil, and boil 1 minute, or until the sugar is dissolved. Add the pears, adjust the heat so the liquid gently simmers, and simmer the pears until just tender, about 8 to 10 minutes. Remove from the heat and let the pears cool to room temperature in the poaching liquid. Cover and store in the fridge in the poaching liquid until needed (pears can be made a day or two in advance).
To make the sauce, pour 3/4 cup of the pear poaching liquid into a small pot. Whisk in the cornstarch until dissolved; mix in the blueberries and lemon zest. Set over medium-high heat and bring to a simmer. Simmer 1 to 2 minutes, or until the sauce is lightly thickened. Serve the sauce warm; or cool to room temperature, refrigerate and serve cold.
To serve, cut pears in half and set 2 halves on each of 4 dessert plates, spoon on the sauce, garnish with mint and serve.
Recipe Options: Instead of blueberry sauce, top the pears with chocolate sauce. Simply place 3/4 cup whipping cream in a small pot and bring to a simmer. Whisk in 3 oz. of chopped semi-sweet chocolate and stir until melted and well incorporated into the cream. Spoon the sauce over the pears and serve.