DIRECTIONS

Heat 1 tablespoon butter in a 12-inch skillet over moderately high heat until foam subsides, then lightly brown bread in butter on both sides. Put toasts on plates and top with mesclun.

Add 1 tablespoon butter to skillet, then cook shallot, stirring, over moderate heat until softened and beginning to brown, 2 to 3 minutes. Add vinegar and cook, swirling skillet frequently, until vinegar is reduced to about 1 tablespoon. Add oysters and remaining 3 tablespoons butter and cook, swirling skillet frequently, until oysters are plumped and butter is incorporated into sauce, about 2 minutes.
Remove from heat and season with salt and pepper. Spoon oysters and sauce over mesclun.