Preheat oven to 350 degrees F. Using baking spray, grease a 9 x 9-inch baking pan.
In a mixing bowl mix together brownie mix, egg, milk, and oil. Mix well until blended.
Pour the batter into the baking pan.
Spoon the dulce de leche over the batter and run a table knife or a toothpick through the mixture to slightly incorporate the dulce the leche with the brownie batter.
Bake for 30-35 minutes or until a toothpick inserted 2 inches from the edge of the pan comes out clean.
Let brownies cool in the pan for about 10 minutes, then transfer to a cooling rack.
Cut into squares. Drizzle with additional dulce de leche if desired and serve.