Broiled Shad with Shad Roe Mousse

INGREDIENTS

• 1 sweet white wine, such as muscadine, Sauternes, or oloroso Sherry
• 1/3 cider vinegar
• Kosher salt
• 1/4 turmeric
• 1 shad roe (2 lobes, 10 to 12 ounces total), each lobe split down the middle
• 1 1/2 honey
• 2 finely chopped bright, tender herbs, such as dill, basil, and mint
• 2 freshly ground black pepper, plus more to taste
• 2 fresh lemon juice (about 1 small), plus 2 lemons, cut into wedges, for garnish
• 1/3 heavy cream
• 3 large egg whites
• Unsalted butter for greasing the bowl
• 1 1/2 flaky sea salt, such as Maldon
• 2 (14-ounce) skin-on shad fillets, scaled, at room temperature
• 2 peanut or vegetable oil
• 2 bunches watercress or pea shoots, for garnish