Classic French Mignonettes combine vinegar, shallots, salt & pepper.
Usually the mignonette sauce is served in a small bowl with a small spoon, alongside the oysters on a platter (or as the French say, "plateau de coquillages"). People can scoop a small amount of the mignonette (1/8 of a teaspoon or so) onto their oyster before eating. One can experiment with color by mixing various portions of white and red wine vinegars.
1/2 cup minced shallots (about 2 1/2 ounces)
1/4 cup white vinegar
1/4 cup clear, unseasoned rice vinegar (if using seasoned rice vinegar, omit the sugar and salt)
1/8 teaspoon sugar
1/8 teaspoon salt
1 1/4 teaspoon finely crushed white peppercorns (do not use pre-ground or powdered white pepper)
Finely mince the shallots:
Peel and coarsely chop the shallots. Put them into a food processor and pulse a few times, until the shallots are finely minced, but not mush, with pieces no smaller than the tip of a match.
You can also finely mince by hand if you wish. The advantage of using a food processor is that the food processor bowl captures all of the liquid released by the shallots as they are minced, which will enhance the flavor of the mignonette.
Stir in white vinegar, rice vinegar, sugar, salt:
Place the minced shallots and any liquid released from them in a non-reactive bowl. Add the white vinegar, rice vinegar, and sugar and salt. Stir with a fork.
Add the freshly crushed white pepper. Stir with a fork.
Cover with plastic wrap and chill in the refrigerator for a minimum of 4 hours. For best results, store for at least 2 days before using.
The mignonette flavor will be better blended the longer it sits. You may notice that the crushed white peppercorns may sink to the bottom of the bowl as the mignonette rests. If you see this, just give it a little stir.
The mignonette will last up to a month in the refrigerator.To serve, shuck the oysters. (Here is an excellent video by Serious Eats on How to Shuck an Oyster.) Make sure that the oyster is loose in the shell before serving.