Preheat the oven to 425 degrees. 

Remove the crusts from the fridge and place them on a lightly floured surface or in between two pieces of waxed paper (my preferred method). Roll out each pie crust to about a 12 inch round circle. Place one of the rounds in a 9 inch pie dish and prick the bottom with a fork. Here you can either trim the edges so they're smooth, use a fork to make a pinprick design on the edges, or use a thumb pressed between two fingers to scallop the edges. Place the crust in the fridge while you continue with the other steps.

Use a cookie cutter to cut out your desired shapes from the other pie crust. Place them on a baking sheet and put in the fridge to chill while you prepare the filling. You won't need the entire second crust to top the pie. Roll up and cut out any scraps and use them to make pie crust cookies. 

Combine all the fruits, sugar, lemon juice, and flour in a bowl. 

Pour the filling into the chilled pie crust. Top the fruit with the cut outs, overlapping them slightly but leaving plenty of pockets for steam to escape. Brush the top and edges with milk then sprinkle with coarse sanding sugar. 

Place the pie on a baking sheet lined with parchment paper for easy clean up (there WILL likely be leakage!). Bake at 425 degrees for 15 minutes then lower the heat to 375 and bake another 30-35 minutes or until golden brown. If you notice any spots getting too browned (this is common for shapes like stars with pointy edges), cover them with a little aluminum foil. 

If you want perfect slices, you'll need to let the pie cool completely before slicing and serving it, but I absolutely love warm pie, so I'm inclined to deal with messy, sloppy slices and serve it while it's still warm (but not piping hot).