Chop the shallots very finely either by hand or using a mini-food processor.
Add the red wine vinegar and mix well. Save refrigerated until ready to use or follow the instructions below to make a granita.
To make a mignonette granita just put in the freezer, let it rest for about 30 minutes, then stir it and put it back. Repeat the process until you have a mix that looks like a cross between crushed ice and fresh snow. Another way to make it is to just let it freeze completely, take it out about 10 minutes before serving and then start scrapping it with a fork.