How A 1940s Cake Mistake Became A San Francisco Dessert Staple

If you have a sweet tooth and are roaming San Francisco trying to satisfy that craving, you might keep an eye open for a rather unusual cake. It sort of looks like it's covered with little fragments of wood or golden-brown lava rocks with pale frosting peeking through from beneath. This sweet, luxurious, and shockingly crispy cake is known as the Coffee Crunch Cake. Much like California's iconic Mission-style burrito, this dessert is a San Francisco original.

Originally dubbed the Koffee Krunch Kake, this confection consists of a layered lemon-vanilla sponge cake with whipped cream frosting that's been infused with coffee. The fractured-looking outside is made from a crushed, bittersweet honeycomb coffee candy. Eating it is a textural experience like no other, and the flavors contrast light sweetness with hints of bitterness from the coffee. You can find it at bakeries and sweet shops throughout the city, though many eateries put their own slight spin on it.

Even if you've never heard of it before, this is hardly a new treat. The dessert was first invented in the mid-1900s and has survived with only small alterations since then (depending on which bakery you buy it from). What's more, this cake was invented because of an unexpected mistake involving a confectioner who messed up a batch of candy. It may well be one of the best foods created by accident.

Blum's first opened in 1892 as a confectionery which soon moved to the corner of Sutter and Polk in San Francisco. It was founded by Simon and Clemence Blum from New Orleans and specialized in candies, though it also sold meals. It would be a solid 50 years before the coffee crunch cake first hit shelves.

The cake's creation came about one fateful day during the 1940s. One of the employees at Blum's overboiled some of the soft coffee candy, rendering it unfit for sale. Rather than waste it, baker Ernest Weil broke up the too-hard candy into small pieces and decorated the outside of a cake with it. These candy pieces created a coating of honeycomb fragments and crumbles, giving the otherwise soft, moist cake a crunchy component. It was such a hit that the bakery began serving it regularly. Blum's continued to do so until it finally closed in the 1970s.

Even though the original Blum's is now gone, its memory lives on and so does its cake. Bakers who previously worked at the spot passed on the recipe and now a few shops in the area sell their own version. Yasukochi's Sweet Stop, in particular, has been making the cake since 1974, and supposedly got its recipe from one of Blum's bakers. If you want to taste the real thing, that's one San Francisco eatery you absolutely must visit at least once.

Of course, if you're handy in the kitchen, you could take a shot at baking one at home. A few online sources claim to offer the original recipe with some small differences between each. It's an intricate recipe, should you decide to look one up, and you might think it's a complicated dessert not worth making at home. But if you're not in San Francisco, it's the only way you'll get a taste.

The cake uses a simple sponge or angel food base flavored with a teaspoon of vanilla and a tablespoon of fresh lemon juice with a little grated lemon zest as well. You'll want to slice the cake into four even layers. For the frosting, you'll need heavy cream, sugar, vanilla, and coffee extract or granules. Whip those together until they form soft peaks, then put some between the layers and all over the outside.

The real challenge, however, is the honeycomb candy. You'll need to combine strong-brewed coffee with sugar and corn syrup over heat until it's thoroughly mixed. Once it boils and starts to become clear, increase the heat and get the candy to around 275 degrees Fahrenheit. Stir in baking soda off the heat to make it foamy, then pour it onto an oiled baking sheet. Once it's cooled completely, shatter it into little pieces, then coat the outside of the cake with the candy. The crunchy bits are delicate and start to soften when wet, so you'll want to eat this cake on the same day it's made. Given how delicious it is, though, that shouldn't be a problem.