Sift together 1 ½ cups flour, white sugar, baking powder, and salt.
In another bowl, whisk together the egg, milk, oil, and vanilla.
Fold the bowl of dry ingredients into the wet mixture.
Spread batter across the bottom of a greased 9x11 pan.
Sprinkle peaches evenly over batter.
In your now empty dry ingredients bowl, combine remaining 2 ½ cups flour, brown sugar, and cinnamon.
Pour melted butter on top and stir.
Sprinkle over batter, breaking into large crumbs as necessary.
Bake for 15 minutes, rotate pan and bake for another 15 minutes.