If you end up with leftover champagne after a party, use it to make champagne vinegar -- the base for a tasty vinaigrette.
In a small bowl, combine mustard and vinegar; whisk together. While whisking constantly, slowly drizzle in olive oil. Season with salt and pepper.
To make homemade champagne vinegar, store leftover champagne in an open, widemouthed jar at room temperature. In a few weeks, it will be vinegar.