Preheat grill to medium, about 400-450 degrees F (205-230 degrees C). Lay out a very large piece of heavy-duty foil, enough to bring up long sides and close over salmon. If you are using cut salmon fillets, lay out individual large pieces of foil. Place Salmon Fillet (2 pound) on, skin side down, and set aside.
In a small microwave-safe bowl melt Butter (1 tablespoon). Add Apricot Preserves (1/4 cup), Whole Grain Mustard (1 tablespoon), and Dijon Mustard (1 tablespoon). Mix well. Remove 2 tablespoons of mustard sauce and set aside to use after salmon is cooked.
Brush on remaining mustard sauce on top of the salmon. Fold up the longer sides and roll together with the seam on top. Roll up the shorter ends to close and make a packet.
Place on grill, cover, and cook for 10 minutes. While salmon is cooking preheat broiler and place oven rack in top position. It's best to err on the side of undercooking the fish. Salmon will finish cooking under the broiler.
Open foil, brush reserved marinade on top and broil for 1-2 minutes, or until salmon is cooked completely and top starts to bubble. Serve immediately.