Preparation

• Position a rack in the center of the oven and heat the oven to 350° F. Lightly butter a 9×2-inch round cake pan. Line the bottom with a parchment round cut to fit the pan, lightly flour the sides, and tap out the excess.
• 在一个中等大小的碗里,搅拌面粉、玉米粉、baking powder, baking soda, and salt until well blended. In a stand mixer fitted with the paddle attachment (or with a hand mixer), beat the butter, sugar, and lemon zest on medium high until well blended and fluffy, about 3 min. Add the eggs, one at a time, beating on medium speed until just blended and adding the lemon juice with the second egg (the batter will appear curdled; don’t worry). Using a wide rubber spatula, fold in half the dry ingredients, then the buttermilk, and then the remaining dry ingredients. Scrape the batter into the prepared pan and spread evenly. Bake for 15 min.

Meanwhile, make the topping.

• Combine the blueberries, sugar, and flour in a small bowl. Using a table fork, mix the ingredients, lightly crushing the blueberries and evenly coating them with the flour and sugar. After the cake has baked for 15 min., slide the oven rack out and quickly scatter the blueberries evenly over the top of the cake (discard any flour and sugar that doesn’t adhere to the berries). Continue baking until a toothpick inserted in the center of the cake comes out clean, another 23 to 25 min.
• Let the cake cool on a rack for 15 min. Run a knife around the inside edge of the pan. Using a dry dishtowel to protect your hands, lay a rack on top of the cake pan and, holding onto both rack and pan, and invert the cake. Lift the pan from the cake. Peel away the parchment. Lay a flat serving plate on the bottom of the cake and flip the cake one more time so that the blueberries are on top. Serve warm or at room temperature.