Get Your Envelopes Ready
Using your fondant roller, some of your white gumpaste to be as paper-thin as possible. Cut out an envelope with your sharp paring knife, using a real envelope as a template. (Because gumpaste tends to dry very quickly, I suggest to cutting out each envelope one at a time.) Taking apart the envelope, use the flaps as a guide to mark the same lines on your gumpaste envelopes with the tip of your knife. Set aside to dry.
Note: You will need to let this dry for 1-2 days before attaching to your finished cake, so make sure to do this step a few days in advance.