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 15 minutes. Pour the butter into a bowl and add the espresso powder and sugar and whisk until smooth. Whisk in egg, vanilla, whiskey and sea salt.  Stir in flour. A

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 just cooked. Cool in the pan, and then lift the foil out and cut into squares.