Preheat the oven to 350 ° Fahrenheit. Butter an 8-inch round or square cake pan and coat with cocoa powder. Set on the side as you prepare the brownie batter.
Place the butter in a saucepot on medium heat. Melt all the butter and whisk in the chopped rosemary leaves. Cover pan, remove from heat and let stand for 30 minutes. This will infuse the rosemary flavor into the butter. Strain the butter and rosemary using a sieve, discard the rosemary, and place the butter back into the saucepot onto medium heat.
Add 1/2 cup of the sugar to the butter. Slowly whisk until all the sugar has dissolved. Turn on the heat and set saucepot on the side.
In a medium sized mixing bowl, whisk together the eggs and remaining sugar until smooth. Add the butter mixture to the egg mixture and whisk to combine.
In a large mixing bowl, whisk the rest of the dry ingredients together; all-purpose flour, salt, cocoa powder, and baking powder. Add the butter and egg mixture to the dry ingredients in three parts, mixing with a whisk until all the liquid is incorporated. Add the chocolate chips and fold in using a spatula. Pour the batter into the prepared cake pan.
Bake the brownies for 30 to 35 minutes. Check for doneness by when the top of the brownies set, and you begin to see a few cracks form on the surface. Let the brownies cool while you prepare the salted caramel topping
Place the heavy cream and brown sugar in a small saucepot on medium heat and bring to a boil. Remove from heat and cover to keep warm.
Place a small saucepan on medium heat. Let it heat up, then sprinkle a thin layer of sugar over the pan. Once it starts to melt on the sides, begin whisking from one side, slowly bringing in the rest of the sugar allowing it to melt quicker. Once the first layer of sugar has melted, slowly keep adding the rest of the sugar and whisking until all the sugar has melted and turned into a caramel. Let this caramel come to a golden amber color, and then turn the heat to low.
While continuously whisking, very slowly pour in one third of the cream mixture into the caramel. Be careful as the caramel will bubble and may splatter if you pour too quick. Whisk in another third until incorporated, then whisk the rest of it into the caramel. Once all the cream has been incorporated into the caramel, continue whisking for five to six minutes on medium low heat. You’ll know the caramel is ready once the bubbles begin to thicken up, and if you have a thermometer the caramel should reach 221° Fahrenheit. Remove from heat and whisk in the sea salt.
Pour the caramel into a shallow dish and cover with plastic wrap, making sure it touches the caramel surface to prevent a skin from forming. Let this cool in the fridge for 20 minutes or until thickened enough to spread. Once cooled, pour an even layer over the brownies while they’re still in the pan and smoothen with a spatula or spoon. If you’d like the caramel to further set, place the brownies into the fridge for another 20-30 minutes, otherwise cut into squares and serve!