Preheat the oven to 350°F. Line a rimmed baking sheet with parchment paper.
In a small saucepan, add the wine, butter and Old Bay seasoning and bring to a boil for 3 minutes. Sprinkle the salmon on both sides with salt and pepper. Place on a rimmed baking sheet; pour the wine mixture over. Bake until salmon is just opaque in center, 12 to 14 minutes (depending on the thickness of the salmon). Remove from oven.
Preheat the oven broiler. In a small bowl, combine the mustard and sugar; spread over thee salmon to cover. Broil the salmon until the topping is brown and bubbling, about 3 minutes. Transfer the salmon to platter and serve.
Notes
If you are preparing this recipe as gluten-free, just be sure to use a brand of mustard that is known to be GF.