CAKE

1. Preheat oven to 350 degrees.
2. In a medium bowl, whisk together the flour, baking powder, baking soda, salt, and cinnamon and set aside.
3. Cut 1/4 cup (1/2 stick) of the butter into slices and place in a 9-inch round cake pan. Transfer the pan to the oven long enough to melt the butter and remove. Add the brown sugar to the butter and mix to coat all of the sugar. Return the pan to the oven for about 30 seconds to completely melt the sugar into the butter. Mix the butter and brown sugar together with a spatula and spread evenly across the bottom of the pan. Arrange the peach slices over top of the butter/brown sugar mixture, placing them in concentric circles, starting at the outer edge of the pan and working inwards. Overlap the slices as you go, and place any small pieces anywhere they will fit.
4. In the bowl of a stand mixer fitted with the paddle attachment,  beat the remaining 1 stick (1/2 cup) of butter on medium high speed until light and creamy, about 1 minute. Add the granulated sugar, egg yolks, and vanilla and beat for about 1 minute on medium speed. Add the dry ingredients and buttermilk in three additions, starting and ending with the dry. Beat just until the dry ingredients are incorporated. Do not over mix. Set aside white you beat the egg whites.
5. Add the egg whites to a medium bowl. Using a hand whisk, whisk the egg whites until they form soft peaks. This will take about 2 minutes. Alternately, you can use a hand mixer. Using a spatula, gently fold the egg whites into the cake batter. Stop folding when there are just a few little streaks of egg white showing in the batter. Do not over mix.
6. Using an offset spatula, spread the batter evenly over the peaches. Gently tap the pan on a counter to remove air bubbles.
7. Bake the cake for 50 to 60 minutes until it is a dark golden brown on top, it springs back when touched in the center, and a toothpick test comes out clean. Ovens vary, but mine took the full 60 minutes to bake.
8. Allow the cake to sit for 5 minutes. Run a sharp knife around the edges to loosen the cake from the sides and transfer the pan to a wire rack to cool for an additional 20 minutes. Run a knife around the edges one more time. Gently shake the pan up and down a few times, and invert the cake onto a cake plate. See notes below on inverting tips.*
9. Serve with a dollop of whipped cream on the side or ice cream.
10. Refrigerate leftovers for up to 3 days.

WHIPPED CREAM

1. Add the ingredients to the large bowl of a stand mixer fitted with the whisk attachment, (or use a hand mixer). Place an old towel over the mixer to prevent splattering when you first start mixing. Mix on medium speed for a few seconds, then increase the mixer to high until soft peaks form.
2. Place a large dollop beside of each serving of cake.
3. Refrigerate leftover cream for up to 2 days.