1 1/2sticks (6 ounces) unsalted butter, cut into pieces
4ouncesunsweetened chocolate, chopped
1 1/2cupsgranulated sugar
3large eggs plus 1 egg yolk
1teaspoonvanilla extract
3/4cupall-purpose flour
1/4teaspoonfine sea salt
3/4cupsweetened condensed milk
Instructions
Preheat the oven to 350°F. Line an 8x8-inch baking pan with foil and spray with nonstick cooking spray.
In a large microwave-safe bowl, combine 1 cup chocolate chips, butter, and unsweetened chocolate. Heat in the microwave for 1 minute then stir. Continue heating in 30-second bursts, stirring between each burst, until the mixture is melted and smooth but not scorched. Remove from the microwave and let cool slightly.
In a large bowl, use an electric mixer to beat the eggs and sugar on medium-high speed until light and thick, about 3 minutes. Beat in the vanilla extract. Stir in the cooled chocolate mixture with a rubber spatula. Add the flour and salt, folding gently until well combined. Pour half of the batter into the prepared baking pan. Bake for 10 minutes.
Sprinkle with the remaining cup of chocolate chips and pour the sweetened condensed milk over the top. Pour the remaining batter over. Return to oven and bake for about 35 minutes, or until a tester comes out with moist crumbs still attached. Do not overbake. Let cool to room temperature then place in the fridge to chill. The brownies are easiest to cut when chilled and can be served chilled, at room temperature, or warmed in the microwave.
Notes
Due to several readers experiencing issues with the brownies not baking or setting properly, I've added to the recipe an extra baking step to ensure that bottom layer will set and I've also slightly reduced the amount of condensed milk.