Preheat oven to 350º. Butter the sides and bottom of an 8 x 8 inch baking pan. Line the bottom with a sheet of parchment paper, and butter the parchment; set aside.
In a medium bowl, whisk together the flour, salt and cocoa powder; set aside.
Place the chocolate and butter in a microwave safe bowl and microwave on medium power for about 2 minutes, whisking every 30 seconds until just melted.
Whisk sugars into warm chocolate mixture until incorporated.
Add three eggs to the chocolate mixture and whisk until just combined. Add the remaining two eggs and whisk until just combined. Stir in the vanilla.
Fold the dry ingredients into the wet ingredients until there is just a trace of the flour mixture still visible. Be careful not to over mix.
Pour half of the brownie mixture into the pan and smooth the top with a spatula. Drizzle the dulce de leche over the brownie layer avoiding the edges. Use an offset spatula to spread the dulce de leche evenly across the brownie layer. Scoop the rest of the brownie batter over the caramel layer smoothing with a spatula.
Bake the brownies for 30 minutes. The brownies are done when the toothpick comes out with a few moist crumbs. Remove from the oven and place the pan on a wire rack; allow to cool completely to room temperature before cutting and serving. Refrigerating them for a few minutes will make it easier to cut.