Place a sauté pan over medium heat and heat the oil. Add jalapeños and onion, sauté until caramelized. Add garlic, once it is soft, deglaze with the Riesling. Next add the mustard and mango preserves and bring to a simmer, simmering over low heat for 20 minutes and refrigerate until completely cool.
Place the salmon, skin side down on the planks, and season with Plowboy's Fin & Feather. Place a rosemary sprig on each fillet, and coat the salmon with the mango mixture. Place the plank on the grill, over direct heat. When the plank has begun to smoke, move the plank to indirect heat to finish. Cook the salmon to an internal temperature of 140° F (use the Maverick PT-100 thermometer for fast and accurate temperature readings); remove from grill and let sit for 2 to 3 minutes before serving.