In a large saucepan add the peaches, ¼ cup of sugar, water, and corn starch and stir to combine. Cook on medium heat for around 5 minutes, stirring occasionally, until thickened. Then transfer to a 2 quart baking dish.
Topping
While the peaches are cooking add the flour, 2 Tablespoons of sugar, baking powder, salt, and cinnamon to a mixing bowl and whisk to combine. Using a pastry blender or forks cut in the butter until coarse, pea sized crumbs form.
In a separate bowl stir together the egg and milk then pour into the flour mixture and stir until just combined.
Spoon the topping on top of the hot filling and bake for 20 to 25 minutes until golden brown.
Let cool for 30 minutes to an hour before serving to allow the filling to thicken.