Preheat oven to 350°F (175°C). Line a 9×13-inch pan with parchment, leaving overhang for easy removal.
In a medium bowl, beat butter, sugar, salt, and vanilla until creamy.
Add flour and mix until a soft dough forms. Start with a spatula, then switch to your hands if needed, just don't overmix.
Press evenly into the prepared pan (use a measuring cup to flatten).
Bake for 12–15 minutes, just until lightly golden around the edges. While it bakes, make the filling.
