1. Preheat the oven to 350'F (180'C). Line the bottom and sides of an 8-inch (20-centimeter) square cake pan with parchment paper.
2. Melt the chocolate, butter, and cocoa powder together in a bowl set over but not touching a saucepan containing an inch or so of simmering water. Do not let the base of the bowl touch the water. When the butter and chocolate are melted, remove the bowl from the heat and stir well to combine. Let cool for about 5 minutes.
3. In a separate bowl, whisk the eggs, brown sugar, and vanilla until it's a little light and creamy, about 2 minutes. Still whisking constantly, add the chocolate mixture and whisk until well combined. Sift in the flour and gently fold with a spatula or metal spoon just until combined.
4. Spoon the brownie mixture into the prepared pan. Use a teaspoon to add blobs of the dulce de leche Gaucho Ranch all over the surface of the brownies. Run a small sharp knife or skewer around the pan to create a marbled effect.
5. Bake until the brownies are dry on top but still slightly gooey and fudge inside, 25 to 40 minutes. Let the brownies cool in the pan placed on a wire rack. Cut into squares.