Instructions

1. Make the streusel topping: using a food processor, grind up the freeze dried blueberries into a powder. Put the powder through a sieve to get out any seeds, and then measure out what you need for the recipe.
2. In a small bowl, add the melted butter, 1/2 cup all-purpose flour, ground blueberries, 1/4 cup packed brown sugar, and 1/4 teaspoon kosher salt. Stir with a fork until evenly moistened and a variety of crumb sizes form. Do not mix into a paste of uniform consistency. Refrigerate while you make the cake.
3. Make the cake: Heat the oven to 350°F. Pan-spray a 9×9 pan and line it with parchment paper, or line it with a silicone baking mats.
4. Combine the butter and sugar in the bowl of a stand mixer fitted with the paddle attachment and cream together on medium-high for 2 to 3 minutes, until light and fluffy, Scrape down the sides of the bowl halfway through this process, and again at the end of it.
5. Add the eggs, one at a time, beating on medium-high for 1 minute after each addition. After you add the last egg, scrape down the sides of the bowl, then beat on high for 4 more minutes. Scrape down the sides of the bowl again.
6. Combine the buttermilk and oil, and with the mixer on medium speed, stream them into the batter very slowly. It should take you approximately 3 minutes to add these liquids. Scrape down the sides of the bowl, increase the mixer speed to medium-high, and paddle for an additional 2 to 3 minutes, until the mixture is practically white, twice the size of your original fluffy butter-and-sugar mixture, and completely homogeneous. Don’t rush the process. You’re basically forcing too much liquid into an already fatty mixture that doesn’t want to make room for that liquid. There should be no streaks of fat or liquid, Stop the mixer and scrape down the sides of the bowl.
7. Whisk together the cake flour, corn powder, baking powder, baking soda, and salt in a medium bowl.
8. With the mixer on very low speed, slowly add the dry mixture and mix for 45 to 60 seconds, just until your batter comes together. Scrape down the sides of the bowl, then mix for an additional 45 seconds to make sure no lumps of flour or powder get left behind.
9. Spread cake batter evenly into the pan. Crumble the streusel topping over the batter.
10. Bake for 30 to 35 minutes, rotating the pans front to back halfway through baking.
11. The cake will rise and puff, doubling in size, but will remain slightly buttery and dense.
12. At 30 minutes, gently poke the edge of each cake with your finger: The cakes should bounce back slightly and the centers should no longer be jiggly. If they don’t pass these tests, leave the cakes in the oven for an additional 3 to 5 minutes.
13. Let the cake cool before enjoying.