Remove the bottom crust from the refrigerator and fill it with the berry mixture. Tuck the pats of cold butter beneath the top layer of berries. Top with the second piece of dough, and trim both to a 1/2-inch overhang around the pie. Tuck the overhang into a roll and crimp the edge, pressing down to hook some of the dough over the edge of the dish, holding the pie. Cut a hole in the center of the pie, as well as some decorative vents.