- Portion size 12 servings
In small saucepan, heat vermouth with chopped thyme over medium heat; let cool for 10 minutes. Strain through sieve.
Cut four 40-inch (1 m) long pieces of foil; place double thickness on each of 2 baking sheets. Grease foil. Cutting just to skin, cut each piece of salmon into 6 portions; place, skin side down, on each pan. Sprinkle with salt; divide lemon and thyme sprigs over each. Drizzle with vermouth mixture. Enclose in foil and seal to form packet.
Roast in top and bottom thirds of 400°F (200°C) oven, rotating and switching pans halfway through, until fish flakes easily when tested, about 25 minutes. Discard thyme sprigs; scrape off white protein. Serve warm or let cool for about 30 minutes. Discard lemon. Refrigerate until cold. Cover and refrigerate for up to 24 hours.
Basil Mayonnaise: In food processor or blender, puree together basil, mayonnaise, chives, oil, lemon juice and salt until smooth. (Make-ahead: Refrigerate in airtight container for up to 24 hours.) Serve with salmon.