When I make ravioli, I like to make mass quantities and freeze them. I lay them in a single layer on a cookie sheet and freeze before putting them in a freezer bag. The problem is that the tops crack in the freezer, spilling the contents when I put them into boiling water. I use the standard recipe for homemade pasta, the recipe that came with the mixer attachment for making pasta. I don't overfill and I press out the air. Any suggestions?