PPQ: Blueberry Buttermilk Upside-Down Cake

Blueberry Buttermilk Upside-Down Cake
source: heavily adapted from The Pastry Queen by Rebecca Rather

Ingredients:

• 1 cup cake flour
• 1/4 tsp baking soda
• 1/4 tsp salt
• a heavy/slightly rounded 1/8 tsp baking powder
• 1/2 cup buttermilk
• Zest of 1/2 lemon
• 1/2 cup (1 sticks) unsalted butter, at room temperature
• 2/3 cup sugar
• 1 large egg white
• 1/2 tsp vanilla extract
• 1 to 1 1/2 cups fresh blueberries, rinsed and dried (enough to almost cover the bottom of a 9-inch round cake pan)
• Powdered sugar, for dusting

Instructions:

1. Place a baking rack in the center of the oven. Preheat the oven to 350° F.  To ensure the cake releases easily from the pan, spray the bottom and sides of a 9-inch round cake pan with cooking spray, place a circle of parchment paper over the bottom of the pan (on the cooking spray), then lightly spray the parchment paper with more cooking spray.
2. In a medium bowl, whisk the flour, baking soda, salt, and baking powder together; set aside.  Stir the lemon zest into the buttermilk, set aside.
   
3. In the bowl of a stand mixer fitted with a paddle attachment, beat the butter and sugar on medium speed about 2 minutes, until light and fluffy. Scrape down the sides of the bowl. Add the egg white and vanilla and beat on medium speed for about 1 minute.  Add about one-third of the flour mixture to the batter and beat on medium speed until just incorporated. Add about half of the buttermilk and beat on medium speed until just incorporated. Continue adding dry and wet ingredients alternately, scraping the bowl down and beating until incorporated after each addition. End with the dry ingredients; the batter should be thick and glossy.
4. Spread the blueberries out in the bottom of the pan.  Spoon the batter evenly over the blueberries and using an offset spatula, smooth the batter out to the sides of the pan. Bake for 25 to 30 minutes, until a toothpick inserted into the middle of the cake comes out mostly clean with just a few crumbs on the toothpick and the top is flat and lightly browned.
   
5. Set the cake pan on a wire rack to cool for 10-15 minutes.  Invert the cake onto the rack and allow to cool completely before dusting with powdered sugar and serving.