First, make the crust. Preheat oven to 350F. Lightly grease a 9×13-inch baking pan, or line with parchment paper. In a large bowl, cream together sugar and butter, until fluffy. Beat in egg and vanilla extract. Working at a low speed, gradually beat in flour and salt until mixture is crumbly, like wet sand. The dough does not need to come together. Pour crumbly dough into prepapred pan and press into an even layer. Bake for 20-25 minutes, until base is set and edges are lightly browned. Cool completely on a wire rack before topping.