Preheat an oven to 180c (350f) and prep a parchment paper-lined 8 by 8-inch baking pan.
In a small mixing bowl, add the butter and the dark chocolate. Melt completely in the microwave or on a ben Marie. Let the chocolate mixture cool completely.
Add the sugar, eggs, salt, and vanilla extract. Stir with a whisk until the mixture is combined.
Transfer the mixture into a big mixing bowl.
Sift the cocoa powder and flour into the mixture and lightly fold the dry ingredients into the wet batter. Don’t overmix! You don’t want to develop the gluten in the flour. This step ensures you have fudgy and moist brownies and not dense and dry brownies.
Pour the batter into a parchment paper-lined baking pan and scoop about 8 scoops of dulce de leche on top of the brownie batter.
Using a knife or a skewer, make swirls until you are satisfied with the look of the brownies. Don’t overmix so you can still see the swirls.
Bake in a preheated oven for 25-30 minutes or until the tops of the brownies are crinkly. Make sure you line your baking pan with parchment paper to prevent the brownies to stick to the pan.
Let the brownies cool to room temperature and enjoy! I know it’s extremely tempting to eat these brownies as they are pulled out of the oven, but let these brownies cool for at least 20 minutes so they will be more firm and won’t crumble up. These brownies are extra moist, fudgy, and melt in your mouth delicious, so it will be worth it to wait these 20 minutes.