Man, these were really good. I always am pleasantly surprised when I manage to make a halfway decent dessert, too.
Note: I used the cook-in-the-can method for dulce de leche that the recipe recommends. It turned out fine. If I did it again, I’d cook it for three hours rather than two to get a deeper color.
2 1/2 sticks butter, at room temperature, plus more for greasing
1 cup granulated sugar
1/2 cup plus 2 teaspoons packed light brown sugar
1/4 cup corn syrup
1/2 teaspoon vanilla extract
4 large eggs, at room temperature
3/4 cup plus 2 tablespoons all-purpose flour
1 cup Dutch-processed cocoa powder
1/4 teaspoon table salt
1 cup homemade or storebought dulce de leche
Flaky sea salt, such as Maldon, for sprinkling
Adjust oven rack to middle position and preheat oven to 350°F. Butter a 10- by 6-inch brownie pan and line the bottom and long sides of the pan with parchment paper. Note: I could not figure out what size baking pan this recipe was talking about. I used a normal 9×9 pan.
Using an electric mixer, beat butter until creamy and lightened in color, about 1 minute. Add granulated and brown sugars, corn syrup, and vanilla and mix until incorporated. At eggs one at a time, mixing after each addition until incorporated.
In a small bowl, stir together flour, cocoa powder, and table salt. Add dry ingredients to butter mixture, and, using a rubber spatula, fold until mostly incorporated. Beat batter with electric mixer until smooth, about 30 seconds.
Pour batter into the prepared pan. Dollop spoonfuls of dulce de leche onto the batter, using a knife to swirl gently to partially mix the two together (be careful to keep the dulce de leche on top as you swirl).
Bake for 15 minutes, then sprinkle with sea salt. Retun to oven and bake until the edge is set but the center is still a bit soft, about 20 minutes (note: mine took closer to 28 minutes, but my oven tends to run low). Let the brownies cool at room temperature in the pan, then cut and serve.