Put the pickling onions in a bowl and pour boiling water over them. Leave for 2–3 minutes, then peel.
Add the drained raisins, the chopped tomatoes, thyme sprigs, lardons and peppercorns. Cook gently until the liquid has evaporated, about 5 minutes.
Add the remaining olive oil and then the mushrooms. Stir them round a few times. Cook fairly briskly for 5 minutes, then add the wine and the lemon juice.
Season and cook over a low heat for 20 minutes, uncovered, remembering to stir them occasionally. Remove the twiggy parts of the thyme branches and allow to cool. Serve just warm or at room temperature; they make a refreshing first course.