Preheat oven to 400. Place a heavy duty rimmed baking sheet in the oven as it preheats.
Have ready an unbaked pie crust in a 9 inch deep dish.
In a large bowl, stir together the sugar, flour, cinnamon, nutmeg, lemon and salt. Add 5 cups of blackberries and stir to coat.
Put the filling in the crust and try to pat it down a bit. At this point you can decide if you need more blackberries. Dot with butter.
Roll out remaining crust and lay over pie. Seal edges, then cut a few slashes to release steam. Alternatively, use a cookie cutter and cut out circles, then lay circles of dough decoratively over top.
Set on the hot baking sheet and bake 30 minutes at 400 degrees F.
Reduce heat and bake for another 25 to 30 minutes at 350 degrees F.
Let the pie cool for several hours, then chill briefly. Return to room temperature before serving.