Preheat the oven to 350°F. Line an 8-inch by 8-inch pan with parchment paper. (If you lightly spray non-stick spray on the bottom and sides of the pan, the parchment will stick to the pan. Do not grease the top of the parchment paper.)

In a large saucepan, melt the butter over low heat. Once fully melted, increase the heat to low-medium to cook the butter, stirring frequently with a rubber spatula or wooden spoon. The butter will start popping and crackling and then start foaming. The part of the butter that will start browning is the milk solids which will be on the bottom of the pan. This is why you need to keep stirring and lifting the spatula or spoon out of the pan to see what stage it is at. Once you have nicely browned specks on the bottom of the pan, remove the pan from the heat and immediately pour the butter into a heatproof bowl to stop it from cooking any further. (Be careful not to overcook the butter. It can go from brown to burnt very quickly.) Allow the butter to cool to room temperature. Set aside the saucepan to also cool.

In a small bowl, combine the flour and salt.

Pour the room temperature butter back to the large saucepan. (If the remaining drops of brown butter on the saucepan reached the burnt stage, do not use the saucepan to mix the batter. Instead, use a large, clean bowl.) With a wooden spoon or spatula, mix in the sugar, brown sugar, milk, and vanilla. Add the eggs and mix until fully combined.

Add the dry ingredients and mix just until fully combined. Mix in the chocolate chips.

Pour into prepared pan.

Sprinkle sea salt on top and bake for 32-38 minutes. The middle should not jiggle and the sides should be lightly browned. A toothpick inserted in the middle should come out clean.

Cool completely in the pan.