Preheat the oven to 350 F (177 C). Line an 8x8 pan with parchment paper along the bottom and two sides.

Add the unsalted butter, condensed milk and semi sweet chocolate chips to a heat safe bowl. Heat the butter, milk and chocolate until fully melted and well combined. This can be done as a 'bain marie' or in the microwave. If using the microwave, heat the mixture 30 seconds at a time, stirring between heating intervals until fully melted and combined.

In another bowl whisk the eggs and sugar together until well combined. Vigorously whisk for about 1 minute. Once the eggs and sugar are smooth and really well combined, whisk in the melted sweetened condensed milk, butter and chocolate mixture until smooth and well combined.

Sift in the cocoa powder, salt and flour together into the creamy chocolate mixture. Stir until just combined. Fold in the additional chocolate chips.

Evenly pour the brownies with sweetened condensed milk into the prepared pan.

Bake for about 35 - 40 minutes. The brownies are ready when a toothpick inserted into the center comes out with a few moist crumbs. Start checking at 30 minutes. If the toothpick comes out with wet streaks, the brownies will need another 5 - 10 minutes.

Cool the brownies in the pan for at least one hour at room temperature. When it’s time to serve, remove the brownies from the pan using the parchment paper overhang. Slice the brownies and enjoy.