In a small saucepan, combine 1/2 of the grated ginger, garlic, soy sauce, whiskey, vermouth, and brown sugar. Cook over medium-high heat until it reduces to about half, 8-10 minutes.
Remove from heat and stir in the lemon juice and rest of the ginger. (If your family isn't wild about a strong ginger flavor, then only add 1/2 of the remaining ginger.)
Let the sauce cool.
Preheat oven to 250ºF.
Line a flat baking sheet with parchment paper or brush with olive oil.
Place the salmon on the prepared sheet skin side down and pat dry. Using a pastry brush, brush a some of the glaze over the top.
Let the fish marinate with the glaze for 5 minutes then brush another Tablespoon of the glaze on top and let sit for 5 minutes.
Put the pan in oven and bake for 10 minutes.
Brush another Tablespoon of the glaze on top of the salmon and roast another 10 minutes.
Continue cooking and repeating with the glaze until the fish is cooked through to your liking. For fish that is about 1-inch thick, it may take 30 to 40 minutes, depending on how well done you like your fish.
Serve garnished with the minced scallion, if desired.