Whisk 1 c sour cream, 1/3 c chopped fresh dill, 3 tbsp finely chopped onion and 2 tbsp Dijon mustard in small bowl to blend. Season sauce to taste with salt and pepper. Let stand at room temperature 1 hour. Preheat oven to 400°F. Lightly oil baking sheet. Place salmon, skin side down, on prepared sheet. Sprinkle with 2 tsp minced garlic, salt and pepper; spread with 1/3 cup sauce. Bake salmon until just opaque in center, approx. 20 minutes. Serve with remaining sauce.
Adjustments: Make the sauce with 1/2 sour cream and 1/2 plain greek yogurt and add juice from a whole lemon. Or sauté onions first, then puree them and add to the sauce if you don’t like raw onions or substitute onions with shallots