Preheat oven to 425 degrees. Line a large rimmed baking sheet with foil. Place a metal rack on top of the baking sheet. This will allow the chicken to get crispy on both sides and allow the juices to run off onto the foil. Place the chicken wings in a single layer on top of the rack. Season generously with salt and pepper. Bake for 30 minutes.
Meanwhile, in a saucepan, melt the butter over medium heat. When the butter is bubbling, add the onion and garlic and cook for 1 minute. Pour in the bourbon, birch or maple syrup, and Sriracha. Reduce the heat and simmer for 3 to 5 minutes, or until thick and sticky. Keep warm.
Remove the pan of wings from the oven. Turn the broiler to high. Using tongs, transfer the wings to a heatproof mixing bowl. Pour two thirds of the sauce over the wings and, using the tongs or a wooden spoon, toss the wings to coat. Return the wings to the metal rack. Broil for 6-10 minutes, turning once, or until caramelized on both sides. Drizzle the remaining sauce over the wings just prior to serving.