Preheat: Preheat oven to 400F with rack on middle position. Line a large, rimmed baking sheet with a big sheet of heavy duty foil that's large enough to fully wrap salmon fillet. Set aside.

Make Sauce: In a medium bowl, whisk together the honey, garlic, shallots, mustard, lemon juice, salt, and pepper. Set aside.

Remove Moisture: Use paper towels to dab off all excess moisture from salmon fillet - this step is important, so don't miss it.

Prepare Foil Packet: Place salmon onto foil-lined baking sheet. Evenly spoon most of the honey mixture (reserve ⅓ cup of the mixture for later) over the salmon. Carefully fold all four sides of the foil so that it creates a "packet" that seals tightly closed and won't leak.

Bake: Bake 10-15 min (10 minutes for a salmon less than 1-inch thick, 15 min for thicker salmon) While salmon cooks, transfer reserved ⅓ cup of honey mixture to a small saucepan or microwavable bowl and cook just until the onions/garlic are soft. You'll use this for serving on the side.

Move Rack: Gently open the foil packet, leaving salmon on the foil (it may seem slightly undercooked, which is fine.) Move oven rack to top position under broiler.

Broil: Broil salmon on high for about 3 minutes or until nicely browned on top; if needed, rotate salmon and broil until desired brownness. Watch closely, as top can easily over-brown.

Serve: Serve salmon with reserved/cooked honey sauce. Garnish as desired, with freshly chopped parsley and/or lemon slices.