1/2 cup unsalted butter (1 stick)
1/2 vanilla bean, split lengthwise, seeds scraped (or 1 teaspoon of vanilla extract)
Non-stick spray (optional)
2/3 cup light brown sugar, divided
4 peaches, cored and sliced (not too thin—you want some texture here)
1 1/4 cup all-purpose flour
1/2 teaspoon baking powder
1/2 teaspoon baking soda
1/2 teaspoon ground cinnamon
1/2 teaspoon kosher salt
2 large eggs
3/4 cup buttermilk
Let’s do it!
1. Preheat oven to 350°. Melt the butter in a small pot over medium-high heat. Cook, stirring or whisking occasionally until the butter starts to brown and foam, 2 to 3 minutes. It should smell like toasted nuts and be the color of caramel; add the vanilla bean if you’re using it, and remove the pot from heat to cool.
2. Spray an 8-inch–9-inch cake pan (springform or regular), pie plate, 1.5-quart baking dish, etc., with non-stick spray (you can use softened butter to grease, too). If you are less confident in your upside-down cake-flipping skills, line the cake pan with parchment (leaving some hanging out of the pan for easy lifting after).
3. Scatter half the brown sugar (1/3 cup) on the bottom of the cake pan and top with sliced peaches; set aside.
4. Whisk flour, baking powder, baking soda, cinnamon, salt and remaining 1/3 cup brown sugar together in a medium bowl.
5. Whisk eggs and buttermilk together in a small bowl (or, just add the eggs to the measuring cup you’ve measured the buttermilk in and whisk in there). Add the vanilla extract, if using. Add buttermilk mixture to the dry ingredients, mixing just to blend. (Don’t overmix here, or the cake will become tight and tough.)
6. Remove the vanilla bean if it’s in the butter. Whisk in the vanilla-y browned butter until the batter is smooth and streak-free. (Again, don’t overmix it, just until everything is well blended.)
7. Pour batter over the peaches, smooth the top (although the batter is pretty viscous, almost like pancake batter and should smooth itself), and bake until cake is golden brown on top, pulls away from the sides of the pan and springs back lightly when pressed in the center, 25–30 minutes.
8. Almost immediately (but without rushing or panicking), place a plate on top of the cake pan. Flip it over gently.