Heat oven to 350°F. Line an 8x8 inch pan with foil and butter it.

Melt the stick of butter in a saucepan and cook it, occasionally scraping the bottom and sides of the pan with a wooden spoon or rubber spatula, until it turns deep golden brown and smells like toasted nuts. Remove the whole thing from the stove top to stop in from cooking and continue to scrape until it stops bubbling and let it sit for about 20 minutes. Pour the butter into a bowl and whisk in sugar until smooth. Hopefully it is barely warm or room temperature by now, but let it sit until it is fairly cooled and then whisk in egg, vanilla, and sea salt. You don't want to scramble the egg, so make sure it is semi-cooled. Stir in flour. Also to note - at this point, you can add things like nuts or chocolate chips or dried cranberries. I have done it before, but ultimately these need nothing added to be delicious...keep it simple.

Scrape the batter into the baking dish, it is thick so you will need to spread it around and smooth it out. Bake it for 25 minutes, or until the edges look a little browned and the center looks justttttt cooked. Cool in the pan, and then lift the foil out and cut into squares.