Preheat oven to 350°F (175°C) and grease a 9x9 inch square baking pan.
In a medium bowl, combine flour and granulated sugar; cut in cold butter until the mixture resembles coarse crumbs.
Press the crust mixture firmly into the bottom of the prepared pan.
Bake the crust for 10 minutes, then remove from the oven.
In a large mixing bowl, whisk together the mashed sweet potatoes, brown sugar, eggs, evaporated milk, cinnamon, nutmeg, ginger, vanilla, and salt until smooth.
Pour the sweet potato filling over the pre-baked crust.
Bake for 35 to 40 minutes or until the center is set and a toothpick comes out clean.
Allow the bars to cool completely in the pan on a wire rack before cutting into 16 squares.