Instructions

1. If using frozen peaches, thaw 2 (10-ounce) bags frozen sliced peaches in the refrigerator overnight or at room temperature for about 3 hours. Place 6 tablespoons of the unsalted butter in the bowl of a stand mixer (or large bowl if using an electric hand mixer) and let sit at room temperature until softened.
2. Place the thawed peaches in a colander and set over a bowl or in the sink to drain. If using fresh peaches, halve, pit and cut TK pounds into 1/2-inch wedges (no need to peel, about 3 cups).
3. Arrange a rack in the middle of the oven and heat the oven to 375ºF. Coat a 9-inch round, 2-inch high cake pan with cooking spray.
4. Melt the remaining 2 tablespoons unsalted butter in a large skillet over medium heat. Add 1/2 cup packed dark brown sugar and a pinch of kosher salt and whisk to combine. Keep stirring until the mixture softens and starts to bubble, 2 minutes. Add the peach slices and stir until the juices release from the peaches and the sugar turns into a syrup, about 3 minutes more.
5. Transfer the mixture into the cake pan and arrange the peaches into an even layer.
6. Place 3/4 cup cake flour, 3/4 cup all-purpose flour, 3/4 teaspoon baking powder, 3/4 teaspoon baking soda, 1/2 teaspoon ground nutmeg, and the remaining 1/4 teaspoon kosher salt in a medium bowl and whisk to combine.
7. Add 1 cup granulated sugar to the bowl of butter. Beat with the paddle attachment on medium speed, until light and fluffy, about 2 minutes. Beat in 2 large eggs one at a time, waiting until the first is completely incorporated before adding the second, about 1 minute.
8. Measure out 3/4 cup buttermilk. Turn the mixer speed down to low. Beat in about 1/3 of the flour mixture, then about half of the buttermilk. Beat in half of the remaining flour, then the remaining buttermilk. Finish beating in the remaining flour mixture.
9. Add 3/4 teaspoon vanilla extract and beat until incorporated. Scrape the batter over the peaches and spread into an even layer.
10. Bake until the cake is slightly puffed, the top is dark golden brown, and a tester inserted into the center comes out clean, 40 to 45 minutes. Loosely cover the cake with aluminum foil if the top gets too dark before the cake is ready.
11. Immediately run an offset spatula or butter knife around the edge of the cake. Invert a serving platter over the cake pan. Using oven mitts and grasping both the platter and the cake pan with both hands, invert the cake onto the platter, gently tapping the top to release the peaches. Gently lift the cake pan off and move any peaches that may have stuck to the pan back onto the cake if needed. Let cool 15 minutes before serving warm, or let cool to room temperature.