Line a small (I used a half size) sheet pan with non stick spray and parchment paper. Set aside.
In a saucepan, melt the butter, sugar, salt and vanilla over medium high heat. Stir constantly until the mixture reaches a dark golden brown color, about 10-15 minutes.
Remove from heat and pour into prepared pan. Let cool for at least 2 hours.
Recipe by the modern barista at https://themodernbarista.com/index.php/2016/08/25/paradeisi-blend-no-ii-toffee-almond-bar/