Melt 3 tablespoons butter in a skillet over medium-high heat; add parsley and next 4 ingredients. Sauté 2 to 3 minutes. Add watercress, and cook 2 to 3 minutes or until wilted. Cool.
Pulse parsley mixture in food processor with the remaining 13 tablespoons butter, breadcrumbs, and liqueur until smooth, stopping to scrape down sides.
Add salt, pepper, and hot sauce.
Fill pie pans or a large baking sheet with 2 pounds rock salt. Dampen salt slightly, and arrange oysters on the beds of salt.
Top each oyster with a spoonful of the parsley mixture.
Bake at 450° about 12 to 15 minutes or until lightly browned and bubbly. Serve on a bed of rock salt, and garnish, if desired.
Note: For testing purposes, we used Pernod for anise-flavored liqueur.
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