Melt the chocolate in a stainless-steel bowl placed over a pan of simmering water, being careful not to let the bowl touch the water. Stir in the corn syrup, vanilla, and salt. Remove from the heat and allow the mixture to cool to room temperature, stirring occasionally. The chocolate should come together with the consistency of pie dough and become more flexible as you stir and work it.
Turn the mixture onto a work surface covered with parchment paper and roll to 1/4 inch thick. (If the chocolate taffy sticks to the rolling pin, cover it with a second sheet of parchment or a piece of plastic wrap.) Shape the chocolate into a large disk, then form it into 4 smaller disks. (If the taffy is too soft to hold its shape, chill it for about 20 minutes and it will hold its shape more readily. You can wrap each disk in plastic wrap and then store them in a resealable plastic bag in the refrigerator for up to 1 month, or in the freezer for up to 6 months.)
At this point you can shape the chocolate taffy into just about anything you please. We’re going to explain how to create lovely flowers. First, line a baking sheet with parchment paper.
Using a rolling pin, roll out a disk of taffy on a piece of parchment to between 1/4 inch and 1/8 inch thick. Cut small circles in the taffy using the back of a pastry-bag tip. (If you don’t have a pastry-bag tip, use a bottle top from a milk jug or anything that cuts uniform circles about 1 inch in diameter.)
Separate the circles (which we will henceforth call petals) on the parchment and flatten the outer edges of each petal with the back of a cold spoon until the edges are almost transparent. Peel the first petal off the parchment (a small spatula helps with this job) and roll it tightly, like a cigar. Pick up the next petal and wrap it around the first one, pinching the two together at the base. Each petal should get successively looser and wider, mimicking the way a rose bloom opens. (Six or so petals ought to do the trick.) Place the completed rose on the prepared baking sheet. Repeat with the remaining taffy, rolling the scraps if you like and using them, too. Cover the baking sheet with plastic wrap and refrigerate for up to 1 month or freeze for up to 6 months.