Trim mushrooms, if necessary, and rinse them in cold water. Put mushrooms in a large saucepan; add enough cold water to cover and mix in salt. Cover with a lid; cook to a boiling point;then reduce heat and cook slowly 5 minutes. Drain and pat dry with paper towels.

When cold, pack into 4 sterilized pint jars and sprinkle with equal portions of peppercorns.

Heat oil, vinegar, mace, thyme together to the boiling point and pour over mushrooms. Seal. Store 1 week before using.