Preheat your oven to 350°F (180°C). Grease and flour a 20 x 30 cm (8 x 12 inch) baking pan. In a blender, add the eggs, vegetable oil, granulated sugar, and hot brewed coffee. Blend for about 30 seconds until the mixture is smooth and slightly frothy. Pour the liquid mixture into a large mixing bowl. Gradually add the cocoa powder and all-purpose flour, whisking or stirring until no dry streaks remain. Add the baking powder and gently fold it in with a spatula. Avoid overmixing once the baking powder is added, as that can deflate the batter.

Pour the batter into the prepared pan and spread it evenly. Bake in the preheated oven for approximately 40 to 45 minutes. To check for doneness, insert a toothpick into the center. The toothpick should come out clean or with only a few moist crumbs attached. If the toothpick has wet batter, bake for an additional 3 to 5 minutes. Let the cake cool in the pan on a wire rack while you prepare the topping. A slightly warm cake is fine, but a fully cooled cake helps the brigadeiro set faster.

In a medium saucepan, combine the sweetened condensed milk, cocoa powder, and heavy cream. Whisk until the cocoa is dissolved and no lumps remain. Add the chopped milk chocolate. Place the saucepan over low to medium heat. Stir continuously with a silicone spatula, scraping the bottom and sides of the pan to prevent sticking or burning. Cook until the chocolate completely melts and the mixture becomes smooth, glossy, and slightly thickened. This usually takes 5 to 7 minutes. The brigadeiro should still be pourable and spreadable. Remove from heat and let it cool for about 10 minutes. If it thickens too much while cooling, gently reheat with a splash of milk.

Pour the brigadeiro over the cooled chocolate cake. Use an offset spatula or the back of a spoon to spread it evenly across the entire surface. Work quickly while the topping is still warm and fluid. If desired, sprinkle chocolate shavings, grated chocolate, or chocolate sprinkles on top for extra texture and visual appeal.

Allow the brigadeiro to set at room temperature for 15 to 20 minutes before slicing. For a richer, fudgier texture, chill the cake in the refrigerator for at least 1 hour. Serve at room temperature or chilled, depending on your preference.