Preheat the oven to 350˚F.
Make the Brigadeiro: In a heavy saucepan, place the condensed milk, cocoa powder, and chocolate, and bring to a boil over medium heat, whisking constantly. When the mixture begins to bubble and the chocolate melts, reduce the heat to low and continue whisking for another 3-5 minutes until the mixture has thickened like fudge. You should be able to tilt the pan and the whole batter will slide, leaving the sticky fudge on the bottom of the pan. Slide the batter into a large bowl without scraping it. You don’t want to incorporate any of the thick residues on the bottom of the pan. Set aside.
Prepare the cake batter: In a medium saucepan, melt the butter over low heat. Pour into brigadeiro and whisk vigorously until smooth. At first the mixture will totally curdle and break. You will think this recipe cannot possibly work, but keep whisking constantly until the mixture comes together again emulsified.
In a separate bowl, beat together the eggs, yolks, salt, sugar and vanilla. Add into the brigadeiro and whisk until homogeneous. Add the flour and mix just until blended, using a spatula.
Pour the batter into foil cups filling them almost to the top (leave about ¼ inch). You can prepare the recipe up to this point and refrigerate for 5 days.
Bake in the oven for 7-9 minutes, or until the edges are firm but the center is still soft. Invert onto a dessert plate. Serve with ice cream (pistachio, ginger, coconut or vanilla are all flavors that work well with this dessert).
NOTE: A word of advice about this molten cake: butter and flour the pan really well. It’s so frustrating when the cake doesn’t come out of the pan properly, and part of the cake is still clinging to the pan. So don’t rely on a thin coating of grease spray; use soft butter—not melted—and shake off the excess flour.