Unroll the piecrust on the prepared baking sheet. Arrange pears in a pinwheel shape in the center of the crust, leaving a 1-1/2 inch border of dough exposed. Moving in a clockwise direction, fold the dough toward the center, pleating as necessary. When you're finished, the opening with the pears in the middle should measure about 5 inches wide. Brush the pastry with milk and sprinkle with coarse sugar.