Preheat oven to 375°F. Fold 2 (16x12-inch) parchment paper rectangles in half lengthwise.
Place 3 stalks of asparagus then 2 onion slices, in the middle, and near the fold of each parchment paper.
6 stalks asparagus, 4-6 slices red onion
Drizzle vegetables lightly with olive oil and sprinkle with salt and pepper.
4 teaspoons olive oil, Kosher salt and freshly ground black pepper
Place salmon fillets on the vegetables and drizzle with olive oil. Season the salmon with salt and pepper.
2 (6-ounce) salmon fillets
Lay lemon slices and fresh thyme on the salmon.
6 slices lemon, 4 sprigs fresh thyme
Drizzle each salmon with 1 teaspoon white wine.
2 teaspoons semi-dry white wine
Sprinkle each salmon with 2-teaspoons brown sugar.
4 teaspoons dark brown sugar
Fold the parchment paper over the salmon and vegetables, at the fold. Starting at one corner, crimp the edges to seal the parchment packet. Be sure to fold and seal the edges tightly so no steam escapes.
Brush the tops of the salmon packets with olive oil.
Set the salmon packets on a baking sheet lined with foil.
Bake at 375°F, on the center rack, in the oven for 15-16 minutes, depending on personal preference. Do not open while baking.
Remove salmon from the oven and, carefully, cut open the top of the packet and serve the salmon in the paper. If desired, remove the skin before serving.
Warm the lemon butter and drizzle it over the salmon.