For the Brownies: Preheat oven to 375 degrees F. Butter and cocoa powder (or use white rice flour if you don't have cocoa powder on hand) an 8-inch round springform pan. Wrap the outside of the pan in foil and set it on a baking sheet.
Combine the eggs, brown sugar and granulated sugar in a large bowl. Whisk until smooth. Add the melted chocolate and butter. Whisk until smooth.
Add the dry ingredients and whisk until the batter is smooth. Pour the batter into the prepared pan.
Allow the brownie to cool before you make the caramel sauce. Transfer the brownie to your serving dish.
Carefully set the hot pot into the water bath. (Be sure that the water isn't higher than the pan. You don't want any water getting into your caramel sauce. Cool until sauce has thickened.
Pour a generous amount of caramel sauce onto the brownie. Sprinkle with a little kosher salt. (You will have made more caramel sauce than you can put on your brownie. Store the leftover sauce in the refrigerator.)
Cut and serve.