Preheat oven to 425 degrees. Coat a 9-inch round cake pan with cooking spray and set aside.
In a large skillet over medium heat, melt the butter or margarine. Add the vanilla and sugar, stirring well to mix. Cook for 2 minutes, stirring constantly. Sugar will not dissolve completely.
Add the pears to the skillet and sprinkle with the cinnamon. Cook for 15 minutes, until the sugar turns a golden caramel color.
Transfer the pears, cut sides up, to the prepared cake pan. Pour the hot sugar mixture over the pears, scraping out the pan with a spatula.
Unroll the pie crust and place over pears, crimping the edges rustically, to fit into the cake pan.
Bake for 20 minutes, until crust is golden brown. Cool for 5 minutes.
Invert onto a rimmed serving plate; cut; and serve with vanilla ice cream, if desired.