Preheat oven to 325 degrees. Line a 9×13 inch pan with parchment paper set aside.

In a large double boiler, melt butter then add espresso powder, mixing to dissolve. Add sugar and cook until the mixture becomes smooth and glossy. Remove from heat and allow the mixture to cool for 20 minutes.

In the bowl of a stand mixer, combine the cooled (it can be luke warm) butter mixture and vanilla. With mixing speed on low add one egg at a time, mixing just until incorporated.

In a medium size mixing bowl, whisk together flour, cocoa powder, baking soda, and salt. With mixing speed on low, gradually add dry ingredients. Mix until batter is smooth and flour is well included. Remove bowl from stand and fold in your milk & semi-sweet chocolate chips (leaving a few chips for the top of your batter).

Spread the brownie batter evenly into your baking pan. You may want to warm you dulce de leche un poquito (just a little) if it's a little stiff. With a spatula or spoon drop in 6-9 spoonfuls of dulce de leche (I like to make rows of 3) gently swirl the ducle de leche through the batter with a knife. Sprinkle remaining chocolate chips on top of your brownie batter.

6.Place in oven and bake for 20- 25minutes or until the brownies are set. Remove from oven and let cool for about 35 minutes before cutting. Ahora...Enjoy!