Preheat oven to 375F with a rack in the middle position. Grease a 9×13 inch pan and set aside
In a large bowl, whisk together 3 cups flour, 1 cup sugar, baking powder, and 1/4 tsp salt. Cut in the cold butter with a pastry cutter. Add the lightly beaten egg. Dough will be moist and crumbly, like clumpy wet sand. Firmly press half the dough into the pan. Place the pan in the fridge
Add brown sugar and pecans to the remaining half the dough and mix together by hand. Place in fridge
Combine peaches and lemon juice
Whisk together 1/2 cup flour, 1 cup sugar, 1/4 tsp salt, cinnamon, and nutmeg. Fold flour mixture together with the peaches gently
Spread peach mixture over chilled crust. Sprinkle blueberries over the peaches. Crumble the chilled topping over the filling
Bake for 45 - 60 minutes, or until the top is golden brown. If top is getting too browned, cover with foil; if not getting browned enough, move to a higher rack
Cool completely on a wire rack, then chill uncovered n the fridge until ready to cut and serve. It is easier to cut these once chilled