STEP ONE: The Sauce-To prepare sauce, combine first three ingredients and bring to a boil. Reduce slightly, allowing vanilla flavor to come out. Whisk in butter. Season to taste. Add tomatoes and set aside.
STEP TWO: The Oysters-To prepare oysters, grind pecans and flour in food processor, making "pecan meal." Dredge oysters in pecan meal. Saute in small, nonstick pan with vegetable oil or butter for two minutes on each side over high heat.
STEP THREE: Place four shells on each of four plates, spoon sauce into shells, and place one oyster on top of each.