1. Preheat the oven to 350 degrees.
2. Grease an 8 x 8 baking pan with canola oil (or use a cooking spray) and sprinkle with just a light dusting of all-purpose flour.
3. To make the crust, cream the butter and confectioners' sugar with an electric mixer until light and fluffy. Add the flour, and beat until the dough just comes together.
4. Press the crust mixture into the bottom of your prepared pan and bake for about 20 minutes, or until lightly browned.
5. Remove crust from the oven and place on a wire rack to cool while you make the filling.
6. To make the filling, blend the tofu in a food processor or blender until creamy, about 1 minute.
7. Add the granulated sugar to the tofu, and blend until nice and smooth.
8. Blend in the lemon zest, lemon juice, flour, and cornstarch.
9. Pour the filling over the baked shortbread crust and bake for about 20 minutes, or until the filling is set.
10. Remove from the oven and place on a wire rack to cool.
11. To serve, cut into squares or bars and dust with the sifted confectioners' sugar.
http://www.savvyvegetarian.com/vegetarian-recipes/vegan-lemon-bars.php