Preheat oven to 350°F (175°C). Line an 8x8-inch baking pan with parchment paper, leaving an overhang for easy removal.
In a mixing bowl, combine flour and granulated sugar. Add softened butter and mix until mixture forms coarse crumbs.
Press the crumb mixture evenly into the bottom of the prepared pan. Bake for 15 minutes until lightly golden.
While the crust bakes, whisk together brown sugar, corn syrup, melted butter, eggs, vanilla extract, and salt in another bowl.
If using, fold chopped nuts into the filling mixture.
Pour the filling evenly over the hot crust once removed from the oven.
Return pan to the oven and bake for 15-20 minutes, until the filling is set and bubbling.
Remove from oven and cool completely on a wire rack.
Lift parchment paper to remove squares from the pan, cut into 12 pieces, and serve.