For the glaze:
1/3 cup maple syrup
3 tablespoons whole-grain mustard
1 teaspoon cider vinegar
1/2 teaspoon finely chopped fresh thyme leaves
1/8 teaspoon kosher salt
1/8 teaspoon freshly ground black pepper
For the fish:
4 (6-ounce) skin-on salmon fillets
Vegetable oil, for oiling the grill and the fish
Freshly ground black pepper
1. Heat a grill pan or outdoor grill to medium high (about 375°F to 425°F).
2. Meanwhile, place all of the glaze ingredients in a medium oven-safe frying pan and whisk until combined.
3. When the grill is ready, place the frying pan on the grill, cover the grill, and cook until the glaze just comes to a boil, about 3 to 4 minutes. Using a hot pad or dry towel, remove the pan from the grill; set aside.
4. Pat the salmon dry with paper towels. Brush both sides of the fillets with vegetable oil and season both sides generously with salt and pepper.
5. Rub the grill grates with a towel dipped in oil. Place the salmon on the grill skin-side down, cover the grill, and cook undisturbed until grill marks appear and the skin is starting to crisp, about 2 to 3 minutes. Using a flat spatula, carefully flip the fillets over and brush the skin with some of the glaze. Cover the grill and continue to cook until the salmon is just opaque in the center, about 2 to 4 minutes more. Transfer to a serving plate and serve immediately, passing the remaining glaze on the side.