Blackberry Cake with Cream Cheese Frosting

Ingredients

• 7 ounces fresh blackberries, firm and tart
• 4 ounces unsalted butter, softened to about 60°F
• 5 1/4 ounces sugar
• 1 1/4 teaspoons baking powder, preferably not aluminum free
• 1/4 teaspoon baking soda
• 1/4 teaspoon Diamond Crystal kosher salt; for table salt, use about half as much by volume or the same weight
• 1/8 teaspoon ground cinnamon
• 2 ounces egg whites, brought to about 70°F
• 5 1/2 ounces bleached cake flour, such as Swans Down, sifted
• To Serve:
• 1 batch Cream Cheese Frosting
• Additional blackberries, to garnish

Directions

1. For the blackberry purée, blend the berries in a blender, food processor, or with an immersion blender until no chunks remain. If you prefer a seedless texture, pass the purée through a fine-mesh sieve, adding a couple extra berries before blending to account for what gets left behind. Set aside exactly 6 ounces of fresh blackberry purée, about 3/4 cup or 170g, and use it once it has reached about 70 degrees F, or 21 degrees C. Move the oven rack to the lower-middle position, then heat the oven to 350 degrees F, or 180 degrees C. Grease an anodized aluminum cake pan measuring 8- by 2-inch or 8- by 3-inch, and add a parchment liner.
2. For the cake batter, place the butter, sugar, baking powder, baking soda, salt, and cinnamon in the bowl of a stand mixer with the paddle attached. Start on low just until the ingredients come together, then switch to medium and beat until the mixture looks pale, airy, and soft, about 5 minutes. Stop midway to scrape down both the bowl and the paddle with a flexible spatula.
3. While the mixer runs, add the egg whites gradually, waiting until each addition disappears into the batter before adding more. Turn the mixer down to low, then add about one-third of the cake flour, followed by one-third of the blackberry purée. Continue alternating the remaining flour and purée in the same manner, using thirds.
4. Use a flexible spatula to scrape the bowl and paddle, then mix again on medium for about 3 seconds so the batter is evenly blended. It should be a bright purple color and read between 65 and 68 degrees F, or 18 and 20 degrees C, on a digital thermometer. If that temperature is far off, the ingredients were likely too hot or too cold, which can affect the cake’s texture. If you see streaks, fold the batter gently with a flexible spatula until the color is even.
5. Transfer the batter to the prepared pan, smooth it level, and bake until the cake has risen and feels set, about 30 minutes. Let it cool in the pan for 1 hour, then slide a butter knife around the sides to release it. Turn the cake out onto a wire rack, remove the parchment, and move it to a serving plate to finish cooling completely, about 1 hour. Finish with a batch of Cream Cheese Frosting and a handful of fresh blackberries, then slice with a chef’s knife. Covered in plastic, the cake keeps for up to 3 days at cool room temperature.