One hour prior to cooking salmon, pour pickled blueberries and the brine in a small bowl. Add purple onion to marinate.
Paint salmon fillets with oil, then sprinkle with salt and pepper. Heat grill or broiler. Place fish, skin side down, in foil, and cook until the flesh is caramelized on the outside and just warm on the inside, 3-5 minutes.
To serve, pour 2-3 tablespoons of creme fraiche over each fillet, then sprinkle with pickled onion and top with pickled blueberries. Certain to impress guests!