In a small skillet cook the onion in the olive oil over moderately low heat, stirring occasion-ally, until it is softened and stir in the parsley, the sun-dried tomatoes, the artichokes, the sour cream, and salt and pepper to taste. Divide the mixture among the toasts, mounding it, and broil the toasts on the rack of a broiler pan about 4 inches from the heat until they are browned lightly. Makes 6 canapes, serving 2.