Preheat oven to 190ºC . For crust combine crumbs, sugar and butter and mix well. Press firmly into 23 cm pie-pan covering bottom only. Bake for 8 min., or until the edges are slightly brown. Reduce oven to 180ºC . For filling, combine cheese, sour cream, cornstarch, and sugar in bowl of mixer. Mix until sugar has disolved. Add the butter and vanilla and blend until smooth. Be careful not to overmix, or the filling will become too fluffy and will crack when cooling. Pour the filling over the crust. Bake for 30 to 35 min., or until knife inserted 3 cm from edge comes out clean. Cool 1 hr. For topping, mix sour cream and powdered sugar. Spread mixture over top of cooled cheesecake. Chill or freeze until ready to eat. Recipe By :