Mix softened butter and brown sugar and spread evenly on the bottom of the 9×2 inch pie dish or round cake pan. (Make sure the pan is 2 inches deep) Arrange peaches in a pattern over sugar mixture. Set pan aside.
In a medium bowl whisk together flour, baking powder and salt.
In a large bowl cream butter, sugar and vanilla extract, add egg and beat until light and fluffy, add dry ingredients alternately with buttermilk, beat on low until combined.
Spoon and spread over peaches.
Bake at 350° for 45-50 minutes or until a toothpick inserted in the center comes out clean. Cool for 10 minutes.
Run a knife around the sides, place a platter on top and invert the cake onto the platter.
If any of the peach slices stick to the pan, lift them off carefully and replace them on top of the cake. Serve warm with ice cream or whipped cream.