Preheat oven to 350°F. Lightly spray a 9" x 13" pan with non-stick spray and set aside.
In a large mixing bowl, beat the butter and brown sugar with an electric mixer until light and fluffy. Then beat in eggs and vanilla extract.
In a medium bowl, whisk the flour, baking soda, and salt together.
Gradually add flour mixture to the creamed butter and brown sugar, alternating with the buttermilk. Beat until smooth after each addition.
Gently fold in the peaches with a spatula. Then spread batter evenly into prepared pan.
In a small bowl, combine the sugar and cinnamon. Sprinkle over the batter.
Bake for 38 to 45 minutes, or until a toothpick inserted near the center comes out clean. Metal pans will usually require less baking time than glass. Serve warm.
