How to Make It
In a small baking dish, whisk both mustards with the honey, miso, 1 tablespoon of the vinegar and 1 tablespoon of water. Add the salmon fillets and turn to coat. Cover and refrigerate overnight.
Meanwhile, in a small saucepan, combine 1/4 cup of water and the remaining 1/4 cup of vinegar with the pickling spice, sugar and 1 teaspoon of salt. Bring just to a simmer. Let cool completely, then transfer to a bowl. Add the carrot ribbons and toss to coat. Cover and refrigerate for at least 4 hours or overnight; toss occasionally.
Preheat the oven to 350°. In a large ovenproof skillet, cook the bacon over moderate heat until browned, about 7 minutes. Using a slotted spoon, transfer the bacon to paper towels to drain. Add the potatoes to the skillet and cook over moderately high heat until browned on the bottom, about 3 minutes. Toss the potatoes, season with salt and pepper and bake in the oven for about 15 minutes, until tender. Stir in the bacon and chives and transfer to a plate; keep warm. Leave the oven on; wipe out the skillet.
Remove the salmon fillets from the baking dish; scrape off any excess marinade. In the skillet, heat the oil until shimmering. Add the fillets skin side down and cook over moderate heat until browned and crisp, about 4 minutes. Turn and cook until browned on the bottom, 2 to 3 minutes. Transfer the skillet to the oven and bake for 5 minutes, until the salmon is medium. Serve the salmon with the carrots and the potatoes.