In a bowl whisk together all purpose flour, baking powder, baking soda and salt. Set aside.
Using the paddle attachment of your stand mixer or using your hand mixer, beat sugar and oil till combined. Then add egg, vanilla extract and mix.
Stir in the buttermilk and mix.
Fold the dry ingredients into the wet. Don't dump the entire mix in one go, do it in 3 parts.
Mix till the flour mix is well combined but do not over-mix. Set aside.
Meanwhile melt butter in a pan. Once the butter melts, add brown sugar and cinnamon and let the sugar melt.
Pour the butter-sugar-cinnamon mixture into a 9 inch round pan.
Arrange the cut peach slices on top. I arranged the peaches in 2 layers, just to make it look prettier.
Pour the prepared cake batter on top of the peach slices. Place the cake pan onto a cookie sheet. I place the pan onto a cookie sheet before placing it in the oven so that in case the batter bubbles and spills, my oven remains clean!
Bake at 350 F degrees for 35-40 minutes or till a toothpick inserted in the center comes out clean.
Take out of the oven and let the cake cool down for 20-30 minutes. Place the serving plate on top of the cake pan and flip over. The cake would come out easily.
Serve peach upside down cake with some vanilla ice cream on top!