Salted Caramel Brownies

To make the caramel filling:

1. Combine the sugar and corn syrup with 1/4 cup of water in a medium saucepan, stirring carefully so as not to splash the sides of the pan. Cook over high heat until an instant-read thermometer reads 350F or until the mixture is dark amber in color, 6 to 8 minutes.
2. Remove the pan from the heat, and slowly add the cream (careful, it will bubble up) and then 1 teaspoon fleur de sel. Whisk in the sour cream and set aside to cool.

To make the brownies:

1. Preheat the oven to 350 degrees Fahrenheit. Butter the sides and bottom of a glass or light colored metal 9x13 baking dish. Line with parchment paper and butter the parchment paper.
2. In a medium bowl, whisk together the flour, cocoa powder, and salt.
3. Place the chocolate and butter in the bowl of a double boiler set over a pan of simmering water, and stir occasionally until the chocolate and butter are completely melted and combined. See notes below if you do not have a double boiler. Turn off the heat, but keep the bowl over the water of the double boiler, and add both sugars. Whisk until completely combined and remove the bowl from the pan. The mixture should be at room temperature at this point.
4. Add three eggs to the chocolate mixture and whisk until just combined. Add the remaining two eggs and whisk until just combined. Add the vanilla and stir until combined. Do not overbeat the batter at this stage, or your brownies will be cakey.
5. Sprinkle the flour and cocoa mixture over the chocolate. Using a spatula, fold the dry ingredients into the wet ingredients until there is a just a trace amount of the flour mixture visible.

To assemble and bake:

1. Pour half of the brownie mixture into the prepared pan and smooth the top with a spatula. Drizzle about 3/4 cup of the caramel sauce over the brownie layer in a zigzag pattern, taking care to make sure the caramel does not come in contact with the edges of the pan or it will burn. (There will be caramel sauce left over that you can either serve over the brownies when serving or refrigerate and use for something else.) Use your offset spatula to spread the caramel evenly across the brownie layer. In heaping spoonfuls, scoop the rest of the brownie batter over the caramel layer. Smooth the brownie batter gently to cover the caramel layer.
2. Bake the brownies for 30 minutes, rotating the pan halfway through the baking time, and check to make sure the brownies are completely done by sticking a toothpick into the center of the pan. The brownies are done when the toothpick comes out with a few moist crumbs.
3. Remove the brownies from the oven and sprinkle with the remaining 1 1/2 teaspoons fleur de sel.
4. Cool the brownies completely before cutting and serving. For the best results, let brownies cool for 24 hours for the carmel sauce and brownies to fully meld into something magical. Store wrapped tightly in plastic wrap for up to 4 days at room temperature or 6 days in the fridge.