1 medium red onion, quartered lengthwise, divided
1½ teaspoons pickling spice mixture
1 cup white wine vinegar
½ cup water
¼ cup granulated sugar
2 tablespoons kosher salt
4 chicken thighs (about 1½ pounds)
⅓ teaspoon curry powder
1 teaspoon plus a pinch of kosher salt, divided
½ teaspoon plus a pinch of freshly ground black pepper, divided
½ cup mayonnaise
1 tablespoon plus 1 teaspoon finely chopped chives
1 tablespoon plus 1 teaspoon lemon juice
1 tablespoon finely chopped fresh mint
1 teaspoon smoked salt
4 thin slices sourdough bread
½ Bosc pear, thinly sliced lengthwise into 8 pieces
4 ounces Camembert cheese, sliced into 6 long, thin slices
1. Pickle the onions: Preheat the oven to 500°. Thinly slice three quarters of the red onion lengthwise and add the slices to a large, heat-safe bowl. In a large square of cheesecloth, add the pickling spices, then use butcher's twine to secure the ends into a sachet. In a medium saucepan, add the vinegar, water, sugar, the spice sachet and the kosher salt. Bring the mixture to a simmer over medium-high heat, reduce the heat to medium-low and simmer, stirring occasionally, until the sugar and salt are dissolved, about 3 minutes. Remove and discard the spice sachet and pour the liquid over the sliced onions. Let marinate at room temperature for 30 minutes, then cover the bowl with plastic wrap and refrigerate until chilled, at least 45 minutes.
2. While the onions pickle, make the chicken salad: In a large bowl, add the chicken thighs, curry powder, 1 teaspoon of salt and ½ teaspoon of pepper and toss to coat the chicken. Transfer the thighs to an aluminum-foil-lined rimmed baking sheet and place in the oven. Roast until the thighs are cooked through, 16 to 18 minutes. Remove the baking sheet from the oven and set the chicken aside to cool slightly.
3. In a small bowl, combine the mayonnaise, chives, lemon juice, and the remaining pinch of salt and pinch of pepper. Finely chop the remaining one-quarter of the red onion.
4. Once the thighs are cool enough to handle, remove the skin and set aside. Remove the meat from the bone and coarsely chop the meat and the skin, adding both to a large bowl. Add the finely chopped red onion, mint, chive mayonnaise and smoked salt and stir to combine.
5. Assemble the sandwiches: Spoon half of the chicken salad onto 1 slice of bread and top with 1½ tablespoons of the pickled red onions. Top with 3 slices of the Camembert and 4 pear slices. Top with another slice of bread and toast using a panini press until the cheese is melted and the slices of bread are browned, about 5 minutes (if using a grill pan, toast the sandwiches on each side until the bread is browned and the cheese is melted). Repeat with the remaining bread, chicken salad, pickled onions, Camembert and pear slices. Serve the sandwiches hot.