To make the Dulce de Leche:

1. Pour sweetened condensed milk into an 8×8″ glass baking dish or 9″ glass pie plate and sprinkle with a pinch of salt. Wrap tightly with foil. Place baking dish into a 9×13″ baking dish. Pour water into the 9×13″ pan until water reaches halfway up the side of the 8×8″ dish.
2. Bake at 425 degrees 1hr 15 minutes, or until the color of peanut butter. Check every 30 minute or so during the cook time to monitor its progress. Add additional water to the 9×13″ pan, if necessary. Allow dulce de leche to cool before handling.

For the brownies:

1. In a large saucepan, melt butter and chocolate chips over medium heat until smooth. Stir in cocoa and sugar. Add eggs, one at a time, beating to incorporate after each addition. Add salt and vanilla. Fold in flour until just combined.
2. Pour half of the brownie batter into an 8×8″ baking dish lined with parchment paper. Spoon 1/3 of the dulce de leche mixture over the brownie batter in small clumps. Use a butter knife to swirl the dulce de leche into the brownie batter.
3. Pour the remaining half of the brownie batter into the pan and smooth. Scoop the remaining dulce de leche in small clumps over the surface of the brownie batter and swirl with a butter knife.
4. Bake at 350 degrees for 30-40 minutes until the center is just set or until a toothpick inserted in the center of the brownies comes out clean.
5. Allow to cool completely before slicing.