Preheat the oven to 350°F (175°C). Grease the 8x8-inch baking pan or line it with parchment paper for easy removal.
In a mixing bowl, combine the flour and granulated sugar. Add the softened butter and mix until the mixture resembles coarse crumbs.
Press the mixture evenly into the bottom of the prepared baking pan to form the crust. Bake in the preheated oven for 15 minutes until lightly golden.
While the crust is baking, prepare the filling. In a separate bowl, whisk together the brown sugar, corn syrup, melted butter, eggs, and vanilla extract until well combined.
If desired, fold in the chopped pecans or raisins to the filling mixture.
Pour the filling over the baked crust, spreading it evenly. Return to the oven and bake for an additional 15-20 minutes, or until the filling is set and slightly bubbly.
Once done, remove the pan from the oven and allow it to cool in the pan on a cooling rack.
Once cool, cut into squares.