
Remove the outer dried skin of the shallots. Remove any partially dried out layers as well.
Trim the top off with a sharp knife, but keep the root end intact.
Place the trimmed shallot on a cutting board, and cut the shallot in half top to bottom.
Now place a shallot half with the cut side down on the cutting board.
With a sharp knife, make 2 - 3 mm cuts along the length of the shallot making sure not to cut through the root end, so that the shallot remains intact. See pictures in the post for reference.
Now slice across to create a small dice of shallots. Place the finely diced shallots in a bowl. See recipe notes below about shallots.
Place the black peppercorns in a small mortar and pestle and grind to form coarsely cracked pepper. A pepper mill set at the coarsest setting can be used as well. If you have neither of these options, place the peppercorns between layers of a cloth napkin and crush them gently with a heavy rolling pin or mallet. Set aside.
In a bowl, combine the white wine vinegar / champagne vinegar, and rice vinegar, and shallots. Add the cracked black peppercorns (I add about 1 tsp, but you can adjust the amount to your liking), about ¼ tsp salt, and sugar, and stir until the salt and sugar dissolve.
Taste and add more salt to taste, and up to another ¼ tsp of sugar (if needed). Keep the salt level low, if you're serving this with particularly briny oysters.
Place the mignonette in a glass bowl and cover tightly. Store in the fridge for a minimum of 2 hours, but ideally at least overnight, or up to 24 hours before serving.
Serve with freshly shucked oysters with a small spoon so that guests can spoon the sauce over the raw oysters before enjoying them.