1. Start by cleaning the mushrooms and drying them with paper towels. Then, if they are not already peeled, remove the skin from your tomatoes, cut them into small cubes, and put them in a saucepan along with the white wine, olive oil, lemon juice, and onions.
2. Cook for 3 minutes over high heat, stirring regularly. Then add the mushrooms, tomato paste, thyme, bay leaf, salt, and pepper. Cover and simmer gently for about 15 minutes over low heat, stirring occasionally.
3. Let cool, refrigerate for at least 1 hour, then serve chilled.