Preheat the oven to 450°F (232°C).
Pat the salmon fillets dry and season both sides with salt and pepper.
Heat the olive oil in an oven-safe skillet over medium-high heat until hot but not smoking.
Place the fillets in the skillet, flesh-side down (if skin-on, place skin side up so meat contacts the pan), and sear without moving for 2–3 minutes until a golden crust forms.
Transfer the skillet to the preheated oven and cook the salmon 7–10 minutes more, or until it reaches your desired doneness; thicker fillets may need a bit longer.
While the salmon cooks, combine the mayonnaise, sour cream, minced fresh dill, horseradish, lemon juice, and garlic powder in a small bowl; season with salt and freshly ground black pepper to taste and mix until smooth.
Remove the skillet from the oven using an oven mitt and transfer the salmon to serving plates.
Top each fillet with a generous spoonful of the creamy dill sauce and garnish with fresh dill sprigs, then serve immediately.