Heat 2 teaspoons olive oil in a large cast-iron skillet over medium-high heat. Add mushrooms, 1/4 teaspoon salt, and 1/4 teaspoon pepper; sauté 2 minutes or until mushrooms begin to soften. Add wine, thyme, and juice; reduce heat to low, and cook 5 minutes or until mushrooms are tender. Pour mushroom mixture into a bowl. Stir in truffle oil; cover and keep warm.
Wipe pan dry with paper towels. Pat scallops dry with paper towels; sprinkle with 1/4 teaspoon salt and 1/4 teaspoon pepper. Place cornmeal in a shallow dish; dredge scallops in cornmeal. Heat 2 teaspoons olive oil in pan over high heat. Add scallops; cook 3 minutes on each side or until golden brown. Serve over watercress and mushroom mixture.
Wine note: No matter how they're prepared, scallops have a flavor that's unique, complex, and earthy, while their texture is almost creamy. And while all sorts of white wines work well, there's a European classic that's not to be missed: albariño. Albariños are fresh, superlively, and have light peach, citrus, and almond flavors. Try Burgans Albariño 2002 (Rías Baixas, Galicia, Spain), $12. -Karen MacNeil