Cut lines on the bottom of the peach to make a "+" sign. Now boil your peaches so the skin begins to peel off by itself.
Once the skin is coming off, pull your peaches from the water. Peel off the skin. Cut up the peaches the best you can and put in a mixing bowl. Add your sugar and corn starch to the mixture. Transfer this all to a cast iron skillet.
As your peaches are cooking make your crumble topping. Mix the butter, flour, sugar, cinnamon , and baking powder together. It should, as its name reflects, become crumbly.
Cook this mixture down until the peaches turn a nice amber color. As your mixture is almost cooked, add your crumble. Now bake in the oven for 20 minutes (on 275F). Make sure you don't burn your crumble, everyone will be sad.