Preheat the oven to 375 degrees F. Grease a 13-by-9-inch baking pan with 1/2 stick of the butter.
Roll out the pie crusts on a lightly floured work surface until large enough to cover the baking pan; set aside.
Melt the remaining 1/2 stick butter in a large skillet over medium heat. Add the agave, cinnamon, nutmeg, peaches and 2 pinches salt; mix well. Bring to a simmer, reduce the heat to low and cook for 10 minutes. Remove from the heat and let cool until warm.
Pour half of the peach mixture into the prepared pan and spread in an even layer to cover the bottom. Grate the zest of half the orange onto the peaches. Cover the peaches with one of the pie crusts and bake until light brown, 15 minutes.
Remove the baking dish from the oven and pour the remaining peach mixture over the crust. Grate the zest from the remaining half of the orange on top of the peaches. Top with the second pie crust, then brush with egg wash and sprinkle with cinnamon. Poke a couple of holes in the crust to allow steam to escape (this helps the crust hold its shape and cook evenly). Bake until golden brown and the peach juices start to bubble, 40 minutes.
Serve with your favorite ice cream.