From America's Test Kitchen Season 3: Two Chocolate Cakes
Those who have eaten hot fudge pudding cake know its charms: unpretentious, moist, brownie-like chocolate cake sitting on a pool of thick, chocolate pudding–like sauce, baked together in one dish, as if by magic. Served warm with vanilla ice cream, this cake has a flavor that more than makes up for its homespun looks. But some recipes lack decent chocolate flavor; texture can be a problem, too. Instead of providing enough spoon-coating sauce to accompany the cake, some are dry, with a disproportionate amount of cake, while others are soupy, with a wet, sticky, underdone cake. We set out to master this humble dessert.
Pudding cake is made by sprinkling brownie batter with a mixture of sugar and cocoa, then pouring hot water on top, and baking. To bump up the chocolate flavor, we used a combination of Dutch-processed cocoa and bittersweet chocolate. We also added instant coffee to the water that is poured over the batter to cut the sweetness of the cake. We baked the cake slow and low to promote a good top crust and a silky sauce. And we found that letting the cake rest for 20 to 30 minutes before eating allows the sauce to become pudding-like and the cake brownie-like.
If you have cold, brewed coffee on hand, it can be used in place of the instant coffee and water, but to make sure it isn’t too strong, use 1 cup of cold coffee mixed with 1/2 cup of water. Serve the cake warm with vanilla or coffee ice cream. Leftovers can be reheated, covered with plastic wrap, in a microwave oven.