Preheat the oven to 350°F. Spray an 8-inch pan with cooking spray and then line with parchment paper and set aside.
Cut the butter into 1 tablespoon size pieces and place in a saucepan. Turn stovetop on to medium low heat, slowly bringing the butter to a boil, stirring occasionally. Once boiling, the bubbles will go from big to small and once the milk solids start to turn golden brown, stir constantly until the golden color starts to darken. Immediately remove from the heat and pour into a heatproof bowl.
In a large mixing bowl, combine the butter with the sugar; beat together until well combined. Next add the eggs and vanilla extract and beat until well combined.
Add the dry ingredients to the bowl and beat just until the flour is incorporated. Then add the butterscotch chips and beat until combined.
Pour the dough in a prepared pan and spread evenly. Bake at 350°F for 28-32 minutes or until a toothpick inserted into the middle comes out clean. Sprinkle with sea salt and cool completely prior to cutting.