Preheat oven to 350°F.
Combine flour, ½ cup sugar and baking powder in a large bowl then stir to combine. Add milk and butter and stir until smooth and set aside.
For the fruit filling: In a large saucepan whisk together brown sugar, cornstarch and water until smooth. Turn heat to medium, add peaches and blueberries then switch to a wooden spoon and cook until mixture is thick and bubbly. Add remaining butter and lemon juice, stirring until butter is melted.
Pour mixture into an ungreased 1½ quart baking dish then scoop topping mixture on top. Does not have to be even. Stir remaining 2 tablespoons sugar and cinnamon together in a small bowl then sprinkle on top.
Place baking dish onto a cookie sheet then bake for 30 to 35 minutes, or until a toothpick inserted into the center of the topping comes out clean. Serve with vanilla ice cream.