Blackout Cake — Brooklyn's chocolate-on-chocolate layer cake

i. Origin & history

The cake comes from Ebinger's Baking Company, founded in Brooklyn at the end of the nineteenth century by George Ebinger, a German-born baker, and his wife. Ebinger's grew into a chain of dozens of bakeries across Brooklyn and Queens, famous for its crumb buns, its onion rolls and, above all, its chocolate blackout cake. For several generations of New Yorkers it was the birthday and Sunday cake.

The name is said to date from the Second World War. Brooklyn was home to the busy New York Navy Yard, and during the war the city held civil-defence blackout drills, in which windows were covered and lights turned off so that ships and the coastline would not be silhouetted for enemy submarines. Ebinger's darkest chocolate cake was named in their honour. The exact year it was introduced is not well recorded, but by the post-war years it was the bakery's signature.

Ebinger's closed abruptly in 1972, after financial trouble, and its loss became a piece of Brooklyn folklore. Newspapers printed readers' attempts to reconstruct the cake, and the blackout cake was revived by other bakeries and home bakers, each with its own version. Most accounts describe the original as chocolate layers with a dark chocolate pudding or custard filling and a fudgy frosting, all coated in chocolate cake crumbs; many modern recipes simplify it by using the pudding as both filling and frosting, as here.

Blackout cake belongs to a broader family of American chocolate layer cakes built on devil's food — the dark, moist, cocoa-rich cake that appeared in American cookbooks around the turn of the twentieth century as the opposite of the white 'angel food'. Its cousins on DessertCat include the German Black Forest gateau and the cinnamon-spiced Mexican chocolate cake.

ii. Why it uses hot coffee and a cornflour pudding

The cake gets its depth and colour from cocoa bloomed in hot coffee. Pouring hot liquid over cocoa powder dissolves its cocoa solids and releases flavour compounds that stay locked up in dry powder, giving a deeper, rounder chocolate taste. Coffee adds its own roasted bitterness, which reads as more chocolate rather than as coffee. The batter is very thin — almost like a crêpe batter — and that high proportion of liquid, along with oil rather than butter, is what makes devil's food so moist and tender.

Cocoa, buttermilk and bicarbonate of soda also determine the colour. Bicarbonate raises the pH of the batter, and cocoa darkens markedly in more alkaline conditions; a little extra soda is part of why devil's food is so much darker than a cake made with melted chocolate alone. Dutch-processed (alkalised) cocoa, which is darker and milder, pushes this further.

The pudding is a cornflour-thickened chocolate custard. Cornflour starch granules swell and thicken only once the milk comes to a full boil, so the pudding must bubble for a full minute; under-cooked, it stays thin and can turn runny as it cools. Chopped dark chocolate and butter stirred in off the heat give it richness and a firmer set as it chills, so it is thick enough to spread and to hold the crumbs.

Finally, the crumb coating: one layer of cake is sacrificed and crumbled to cover the outside. It gives the cake its characteristic matte, almost velvety black appearance and soaks up a little of the pudding, so the outside is soft and cakey rather than sticky.

iii. Ingredients

Makes 14 servings · scroll the side panel to adjust

• 225 g plain flour
• 70 g cocoa powder, preferably Dutch-processed
• 300 g caster sugar
• 1½ tsp bicarbonate of soda
• 1 tsp baking powder
• 1 tsp fine salt
• 2 large eggs
• 240 ml buttermilk
• 120 ml sunflower or rapeseed oil
• 2 tsp vanilla extract, for the cake
• 240 ml hot strong coffee
• 750 ml whole milk, for the pudding
• 200 g caster sugar, for the pudding
• 50 g cocoa powder, for the pudding
• 60 g cornflour
• ¼ tsp fine salt, for the pudding
• 150 g dark chocolate (60–70%), finely chopped
• 40 g unsalted butter
• 1 tsp vanilla extract, for the pudding

Dutch-processed cocoa gives the darkest colour and smoothest flavour; natural cocoa works but the cake will be slightly redder and more acidic. Use freshly brewed strong coffee or 2 tsp instant espresso dissolved in 240 ml boiling water; decaf works as well. The pudding needs whole milk for body; semi-skimmed sets more weakly. Use a dark chocolate you would enjoy eating, as it carries the flavour of the filling.

iv. Method

1. Make the pudding first, so it can chill: whisk the 200 g sugar, 50 g cocoa, cornflour and salt in a saucepan, then gradually whisk in the milk until smooth. Bring to the boil over medium heat, whisking constantly, and let it bubble for 1 full minute until very thick. Off the heat, whisk in the chopped chocolate, butter and vanilla until smooth. Pour into a bowl, press cling film onto the surface and chill for at least 3 hours.
2. Heat the oven to 175 °C (350 °F), or 160 °C fan. Grease two 20 cm round cake tins, at least 5 cm deep, and line the bases.
3. Whisk the flour, 70 g cocoa, 300 g sugar, bicarbonate, baking powder and salt in a large bowl. Add the eggs, buttermilk, oil and vanilla and whisk until smooth, then whisk in the hot coffee. The batter will be very thin.
4. Divide between the tins and bake for 30–35 minutes, until a skewer comes out clean and the tops spring back. Cool in the tins for 15 minutes, then turn out and cool completely on a rack.
5. With a long serrated knife, split each cake horizontally into two layers. Crumble the least even layer into fine crumbs with your fingers or a food processor and set aside.
6. Beat the chilled pudding briefly until smooth. Place a cake layer on a plate, spread with a quarter of the pudding, then repeat with the second and third layers. Cover the top and sides with the remaining pudding.
7. Press the cake crumbs all over the top and sides, scattering them generously and patting them in until no pudding shows. Chill for at least 1 hour before slicing with a hot, wiped knife.

v. Tips & common mistakes

• Boil the pudding for a full minute. Cornflour only thickens properly at a full boil. Under-cooked pudding is thin and makes the layers slide.
• Chill the pudding thoroughly. Warm pudding is too loose to spread and soaks into the cake. It needs at least three hours, ideally overnight.
• Trust the thin batter. It looks far too runny, but that is what makes devil's food cake so moist. Do not add more flour.
• Use a deep tin. The batter rises well; tins shallower than 5 cm may overflow.
• Cool the layers completely before splitting. Warm devil's food is fragile and tears. Chilled layers are easiest to cut evenly.
• Make fine crumbs. Large chunks fall off. Rub the cake between your fingers or pulse it briefly so the crumbs press on evenly.

vi. Variations

A fudge-frosted blackout cake, closer to many memories of the Ebinger's original, uses the pudding only between the layers and covers the outside in a dark chocolate fudge frosting before adding the crumbs. A mocha blackout cake adds 1 tbsp instant espresso to the pudding. Blackout cupcakes bake the batter in cases, fill them with pudding and roll the tops in crumbs. Some bakeries add a pinch of salt flakes or a layer of salted caramel for contrast.

For other dark chocolate cakes on DessertCat, try the German Schwarzwälder Kirschtorte, a spiced Mexican chocolate cake or the sugar-free chocolate cake. For a lighter American layer cake, see the golden sponge.

vii. Serving & storage

Serve blackout cake in tall slices, cool but not fridge-cold — take it out 20 minutes before serving so the pudding softens slightly. A glass of cold milk is the Brooklyn way; black coffee or a scoop of vanilla ice cream also cuts the richness. It is a birthday cake and a crowd cake, and a little goes a long way.

Because the filling is a milk pudding, keep the cake covered in the fridge and eat it within 3 days; the crumbs soften slightly with time but the cake stays moist. The cake layers can be baked a day ahead, wrapped and kept at room temperature, or frozen for up to 2 months. The pudding can be made up to 2 days ahead. The assembled cake does not freeze well, as the pudding turns watery on thawing.

ix. More from North American

• Mexican Chocolate Cake — cinnamon-spiced chocolate
• Sugar-Free Chocolate Cake — rich cake without added sugar
• Marble Cake — swirled chocolate and vanilla
• Blue Velvet Cake — red velvet's blue cousin
• Schwarzwälder Kirschtorte — German Black Forest gateau
• Golden Sponge — American yellow layer cake