Preheat the oven to 350oF and line an 8 inch square baking pan with parchment and lightly grease with cooking oil spray.
Put the chocolate and butter in a saucepan set over a low heat and melt together then set aside.
In a large mixing bowl, add the eggs, sugar and vanilla extract and whisk until doubled in volume.
Pour in the melted chocolate and butter mixture and mix until fully combined and a uniform color.
Sift in the flour and cocoa powder and mix on a low speed until just combined.
Pour the brownie batter into the prepared baking pan.
Add a teaspoon of flaky sea salt to the caramel sauce and stir together. Reserve 1/4 cup for later then dollop the remaining caramel sauce on top of the brownie batter. Use the end of a knife (or similar) to very gently swirl it into the brownie batter.
Bake in the center of the preheated oven for 30 minutes. You can test for doneness by insertng a toothpick into the middle of the brownies. It should not come out clean but should not be wet either. The brownies will continue to set in the pan once you take them out of the oven.
Immediately drizzle over the remaining caramel sauce while the brownies are still hot in the pan.
Once cool, remove the brownies from the pan and cut into 9 squares.
Sprinkle each brownie with sea salt, serve and enjoy!