1) Preheat oven to 350 degrees. Bring a large pot of water to a boil. Add the peaches and boil for 30 seconds. Remove and place peaches in a large bowl of ice water. Once peaches are cool, carefully remove the skins. They should come off easily by just pushing back on the skins.
2) Dice peaches into large cubes. Add the peaches, blueberries, sugar, lemon zest, lemon juice, and 2 tablespoons flour to a bowl. Mix until well combined then let rest while you make the crumble. If mixture becomes too juicy, add a little more flour.
3) In a food processor, electric mixer, or using your hands, combine the brown sugar, oats, flour, cinnamon, and cold butter, until mixture comes together and has formed little crumbs the size of peas.
4) Grease the inside of a 9x13 inch baking dish and pour in the peach and blueberry mixture. Evenly sprinkle the crumble topping and bake for 50-60 minutes, until top is lightly browned and crisp, and the fruit is bubbly. Let sit for at least 10 minutes before serving, and top with vanilla ice cream.