Line the dish that you want to use (I used 9x13x1) for fudge with parchment paper, up the sides as well. Lightly spay the paper with cooking spray.

Heat up the water in a double boiler, on medium heat.

Place the butter in the double boiler and when it starts to melt, add chocolate chips and condensed milk.

Stir slowly while the chocolate melts and until the mixture is combined and smooth.

Pour the fudge mixture into the prepared pan.

Heat up Dulce de Leche in the microwave, a few seconds at a time, until liquidy.

Pour over the fudge and swirl it around.

Sprinkle with some sea salt and let it set in the fridge for a couple of hours.