1. Center a rack in the oven and heat to 425 degrees. Bring Champagne and orange juice to a simmer in a medium ovenproof skillet over medium-high heat and reduce by about a third, 3 to 5 minutes.
2. Season salmon with salt and pepper and place, skin-side down, in the skillet. Transfer to oven and roast until fish is just cooked through (centers will be slightly translucent), 8 to 10 minutes.
3. Transfer salmon to plates, keeping juices in skillet, and tent loosely with foil. Return skillet to stovetop, add shallot, and bring to a simmer over medium heat. Remove from heat and whisk in butter and orange zest until butter is melted and sauce is slightly thickened. Drizzle over salmon and serve.