Instructions

1. For the cake, adjust oven rack to middle position and heat oven to 350 degrees. Coat a 9X13-inch baking pan with nonstick cooking spray. Whisk flour, sugar, cocoa, baking soda, and salt together in the baking pan.
2. Make 1 large and 2 small craters in dry ingredients. Add oil to large crater and vinegar and vanilla separately to remaining small craters. Pour water into pan and mix until just a few streaks of flour remain. Use a rubber spatula to spread the batter evenly in the pan if it isn’t level after mixing. Immediately put pan in oven.
3. Bake until toothpick inserted in center of cake comes out with a few moist crumbs attached, about 23-25 minutes. Remove the cake from the oven and let it cool in the pan on a wire rack until cooled completely.
4. Using a bamboo skewer or tines of a fork, poke holes all over the top of the cake. In a glass liquid measure or a microwave-safe bowl, combine the sweetened condensed milk and the chocolate. Microwave for one minute and stir. If not completely melted and smooth, microwave for an additional 30 seconds until melted and smooth. Whisk in the evaporated milk and heavy cream (or half-and-half). The mixture will start out very, very thick. Don't worry! It will thin out as you whisk in the other milks.
5. Slowly pour or ladle spoonfuls of the chocolate mixture over the top of the cake. Let the liquid absorb before adding more. Ladle the liquid onto the cake until all the chocolate mixture has been used. It's ok if there is excess liquid pooled on top of the cake, it should absorb into the cake while it is refrigerated.
6. Cover the cake with plastic wrap and refrigerate for at least 2 hours and up to 24 hours.
7. Serve pieces of the cake with sweetened whipped cream and a dusting of cocoa powder.