Preheat oven to 400 degrees F. In a large baking dish (or you can also use a baking sheet), arrange sliced fennel in a layer in the center of the baking dish (these will be under the salmon). Arrange potato slices along the sides of the baking dish or sheet (so they will be all around the sides of the salmon). Season fennel and potatoes with salt and pepper, to taste. Drizzle olive oil evenly over the vegetables. Place in preheated oven and bake for about 25 minutes, until potatoes and fennel are softened and just starting to brown slightly.
While the vegetables cook, prepare the herb citrus butter and salmon. In a small bowl, combine butter, orange zest, fennel fronds, and rosemary. Spread evenly over salmon filet. Once vegetables are tender and starting to brown slightly, remove from oven. Place salmon filet, butter side up, in the center of the baking dish on top of the fennel. Arrange orange slices on top of the salmon. Place back in oven and cook for about 15-20 minutes, until salmon is cooked through completely (should flake easily and look opaque at the thickest part). Remove from oven. Top with additional fennel fronds, if desired.
Recipe by Wright Family Table at https://www.wrightfamilytable.com/roasted-salmon-with-potatoes-fennel-and-orange/