Whisk the brown sugar, maple syrup, Dijon mustard, cider vinegar, tamari, tomato paste, crushed red pepper, and garlic together in a small saucepan.
Pour the bourbon in as well, whisking it in with the other ingredients.
Bring the saucepan to a simmer over medium-high heat, and then turn it down to medium-low and simmer for 8 to 10 minutes. The sauce will thicken into a glaze and should reduce to about ⅓ cup of liquid.
Strain the glaze into a bowl or measuring cup using a fine-mesh sieve. Reserve a few tablespoons of glaze in a small bowl to serve with the salmon.
Preheat the oven to 425 F and line a baking sheet with nonstick foil.
Transfer the salmon fillets to the foil-lined baking sheet and paint the remaining glaze evenly over the top and sides of the fillets with a pastry brush.
Bake the salmon in the oven for 8 to 13 minutes, depending on the thickness of the fillets.
Move the sheet pan to a rack a few inches under the broiler and broil for 2 to 3 minutes, or until the glaze bubbles and begins to caramelize around the edges.
Serve the salmon with the reserved sauce on the side, and sprinkle it with chopped scallions if desired.