When I was growing up in Kentucky, blackberry jam cake was something that turned up at just about every picnic and potluck I ever attended, usually in the form of a Bundt cake with caramel frosting. It's really just a spice cake sweetened with blackberry jam, but the very concept made me crave a colorful blackberry cake, along the lines of those impossibly pink strawberry cake mixes I saw at the store.
It's an idea I've toyed with over the years, but one I always managed to put off until recently, perhaps because I've had a lot more free time since putting my cookbook to bed. I'm so, so glad that I finally got around to pursuing this childhood dream, because fresh blackberry cake turns out to be outrageously, unbelievably good. It's fluffy, light, and moist, tangy from both fresh blackberries and cream cheese frosting, with a whisper of cinnamon running underneath it all, coaxing out more blackberry flavor than spice (kinda like when I use coriander in blueberry pie).
The technique itself plays by the same rules of my vanilla butter cake, so read up on that if you'd like a deeper dive into the particulars of creaming, ingredient temperature, cake pans, and so on. The difference comes down to a few key ingredients: the liquid, the eggs, and the flour.
Most cakes rely on a high proportion of liquid ingredients (usually dairy) to create a fluid batter, a high-moisture formula that can't accommodate the extra water in a fruit purée. So, in order to cram tons of blackberries into the cake, I knew they'd have to stand in for 100% of the liquid ingredients. Like buttermilk, blackberry purée is acidic enough to tenderize the cake like no other and help it to rise—plus, its flavor and color are off the charts.
The exact shade will depend on the composition of your berries; the pale purple you see in the photo above comes from run-of-the-mill supermarket berries, while the incredible Cookie Monster blue in the video comes from berries I picked up at the farmers market. The cake will have amazing color and flavor either way, but the intensity relates directly to the quality of your berries.
Whatever type of berries you have, the best way to keep their flavor and color bright is to make the cake with egg whites instead of whole eggs. (Yellow yolks + bluish purée = yucky green.) A yolk-free cake may sound like a dieting shortcut, but trust me, there's plenty of richness in the buttery cake and frosting—cream cheese, holla!
* Bleached all-purpose flour is treated through an unrelated process that doesn't alter the flour's behavior, so the two can't be used interchangeably, even if the protein content is similarly low.
With those items squared away, assembling the blackberry cake is pretty simple. Start by making the blackberry purée, which is fast and easy with an immersion blender, but you can blitz the berries however you like. I like a seed-flecked cake; if you'd prefer to strain the purée, be sure to start with a few extra berries to make up for the loss.
Once the purée is ready, cream the butter and sugar until it's fluffy and pale, then add the egg whites, a little at a time.
Pause to scrape the bowl and beater, and resume mixing on low. Add a third of the cake flour, followed by a third of the blackberry purée, and so on until both have been fully incorporated.
This is my favorite part—watching the inky purée stain the batter to a lovely purple shade. To avoid ending up with a tie-dyed cake, it's critically important to scrape the bowl and beater really well, and to continue mixing a few seconds longer to eliminate any streaks of purée.
Scrape into a lightly oiled and parchment-lined eight-inch aluminum cake pan. I've talked in the past about the importance of using a good cake pan, but it's especially true for blackberry cake, which can severely discolor with the wrong type of metal.
As with any cake, anodized aluminum is the best choice to limit browning around the edges, and browning on the top can be minimized with a pan that's three inches deep. (Mine is from Fat Daddio's.) These differences are all the more important when you're baking a beautiful blackberry cake.
Since it won't brown like a traditional cake, bake it at 350°F (180°C) until it's puffed and firm, with an internal temperature of around 200°F (93°C). This will take about 30 minutes, but you may want to start checking on it a little sooner, just to be safe. Let the cake cool about an hour in the pan, as it will be quite fragile while warm, then invert and peel off the parchment.
The cake will still brown slightly on the bottom—that's just the nature of butter and sugar plus heat—but with a reflective aluminum pan and a parchment layer, that crust will turn out delicate, thin, and light.
Since it isn't meant for stacking, there's no need to trim off the dome; simply top the cake with your favorite frosting. I'm a sucker for tangy Cream Cheese Frosting, but lemon or blackberry whipped cream would be excellent as well.
After frosting the cake, finish by piling on all the fresh blackberries you can stand—they'll keep the plastic wrap from sticking during storage or transportation, and, let's be honest, they look pretty awesome.
Like banana bread, this blackberry cake keeps remarkably well at room temperature, so it's a great make-ahead dessert for holidays or when you're expecting company. And, since there aren't any layers to fuss with, it travels well, too.