Recipe courtesy of Patrick McMurray, Owner, Starfish Oyster Bed & Grill.Yield is 2 1/4 cups.
Put onions, olives, and horseradish into a small food processor.
Blend until a nice paste forms.
Transfer to a bowl and mix in ketchup, Worcestershire, Tabasco, lemon juice, cider vinegar, red wine vinegar, salt and sugar.
Stir until smooth.
Put sauce into ramekins and serve with oysters on the half shell.