Technically any pie can be made with a single crust, but some, like traditional apple, and this one, are just better with two. If you really just do not want to do two crusts, I recommend making some type of crumble to put on top. Besides looking nice, the starch on top helps to absorb some of the juice from your cooking berries. Without it there to act as a delicious sponge, you may end up with a pie that is slightly runnier than one would like.