Use a meat tenderizing mallet on a good sturdy table - not the cutting board - to flatten them. Place a large parchment paper, place the half cooked plantain disks on one side. I put all of them from one banana next to each other on one side of the paper. Fold the parchment paper over all of them. Take the mallet and flatten them out one at a time, being careful they don't fly out of the paper. It's a great way to take your stress out!! Or you could use a Tostones Press but I really don't think you need it if you have a good meat tenderizing mallet.