Blackberry Cake With Cream Cheese Frosting

Ingredients

Cake

• 7 ounces fresh blackberries (about 1 1/4 cups; 200g), firm and tart (see note)
• 4 ounces unsalted butter (about 8 tablespoons; 110g), softened to about 60°F (16°C)
• 5 1/4 ounces sugar (about 3/4 cup; 145g)
• 1 1/4 teaspoons baking powder, preferably not aluminum free (see note)
• 1/4 teaspoon baking soda
• 1/4 teaspoon (1g) 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 (about 1/4 cup; 55g), brought to about 70°F (21°C)
• 5 1/2 ounces bleached cake flour (about 1 1/4 cups, spooned; 155g), such as Swans Down, sifted (see note)

Cream Cheese Frosting

• 3 1/2 ounces sugar (about 1/2 cup; 100g); see notes
• 5 ounces heavy cream (shy 2/3 cup; 140g)
• 1 teaspoon (5g) vanilla extract
• 1/8 teaspoon Diamond Crystal kosher salt; for table salt, use about half as much by volume
• 8 ounces plain, full-fat Philadelphia cream cheese, cold (one 8-ounce brick; 225g)

Directions

Cake

1. To Prepare: Using a blender, food processor, or immersion blender, purée blackberries until totally smooth. If seeds bother you, the purée can be strained using a fine-mesh sieve; if you do plan to strain, add a couple extra blackberries to make up for the loss. Measure out exactly 6 ounces fresh blackberry purée (about 3/4 cup; 170g) and bring to about 70°F (21°C) before using.
2. Adjust oven rack to lower-middle position and preheat to 350°F (180°C). Lightly grease an 8- by 2-inch or 8- by 3-inch anodized aluminum cake pan and line with parchment (explanation and tutorial here).
3. To Make the Cake: In the bowl of a stand mixer fitted with paddle attachment (see note), combine butter, sugar, baking powder, baking soda, salt, and cinnamon. Mix on low speed to roughly incorporate, then increase to medium and beat until fluffy and light, about 5 minutes. About halfway through, pause to scrape bowl and beater with a flexible spatula. With mixer still running, add egg whites a little at a time, letting each addition fully incorporate before proceeding to the next.
4. Reduce speed to low and sprinkle in about one-third of cake flour, followed by one-third of prepared blackberry purée. Repeat with remaining flour and fruit, working in thirds as before.
5. Scrape bowl and beater with flexible spatula and resume mixing on medium speed for about 3 seconds to ensure everything is well combined. The batter should look bright purple and register between 65 and 68°F (18 and 20°C) on a digital thermometer. (Significant deviation indicates ingredients were too warm or too cold, which can lead to textural problems with the cake.) If the batter looks streaky or tie-dyed, gently fold with a flexible spatula until streaks disappear.
6. Scrape into prepared pan, spread into an even layer, and bake until puffed and firm, about 30 minutes. Cool directly in pan for 1 hour, then run a butter knife around the edges to loosen. Invert onto a wire rack, peel off parchment, and place on a serving plate until fully cool, about 1 hour. Top with a batch of Cream Cheese Frosting and a handful of fresh blackberries and cut with a chef's knife to serve. Wrapped in plastic, this cake will keep for up to 3 days at cool room temperature.

Cream Cheese Frosting

1. With kitchen temperatures above 74°F (23°C), start by refrigerating the mixing bowl and sugar until they have cooled to 70°F (21°C). At elevated temperatures, these ingredients and equipment can act as a heat source to the cream, preventing full aeration.
2. In the bowl of a stand mixer fitted with the whisk attachment, or using a hand mixer, combine sugar, cream, vanilla, and salt. Mix at medium-low speed until sugar is dissolved, about 2 minutes. Increase speed to high and continue beating until cream is about as thick as Greek yogurt, about 2 minutes longer. Begin adding cream cheese 2 tablespoons at a time; this should take about 30 seconds all together. Once it is incorporated, shut off the mixer. The frosting will look a bit curdled, like cottage cheese; this is the result of incomplete mixing rather than over-whipping, so don’t be alarmed.
3. Thoroughly scrape bowl and whisk, then continue whipping on high until frosting is smooth and light, with only a few small flecks of cream cheese (they will disappear into the frosting over time). This may take 2 to 3 minutes with a stand mixer, or more if using a hand mixer. After whipping, the frosting should be about 60°F (16°C). Use immediately or refrigerate until needed.

Notes

1. In this recipe, aluminum-free baking powder formulations may cause discoloration in the final product.
2. If using an unvarnished aluminum paddle attachment, be sure it’s meticulously clean and free from oxidized residue. If you’re not sure, wipe the paddle firmly with a damp paper towel until no trace of gray remains on the cloth, as this will cause the acidic batter to discolor in the oven. For more information, consult KitchenAid’s Product Help Sheet.
3. The success of this recipe hinges on the unique behavior, pH, and starch content of bleached cake flour; other types of flour will produce a cake that's gummy and dense. For more information, please consult this article on bleached cake flour. This batter is also formulated to the specific pH and moisture content of blackberries; it cannot be made with any other type of fruit.
4. If room temperature climbs above 74°F (23°C) in your kitchen, refrigerate the mixing bowl and beater, along with the sugar, until it's cooled to about 70°F (21°C) before whipping the cream; otherwise, the warm bowl and sugar may inhibit aeration.
5. It seems that due to variations in the formula, not all brands of cream cheese perform equally well in this recipe. For best results, use Philadelphia cream cheese.