Position your oven rack in the middle of the oven, and preheat to 450 F.
Whisk the olive oil (2 tablespoons) and mustard (1 tablespoon) together until smooth.
Pat salmon dry with paper towels, and place skin side down in a cast iron skillet, or on a rimmed baking sheet. Sprinkle with salt (1/2 teaspoon) and pepper (1/4 teaspoon). Press to adhere. Brush the tops with an even layer of olive oil (2 tablespoons) and mustard (1 tablespoon).
Bake salmon until it's dark pink in the center (simply pierce with a fork to check), should be 12-15 minutes but will vary with how thick your filets are.
Sprinkle dried dill (1/2 teaspoon) on top before plating and enjoy!