1. Preheat oven to 450°.
2. Combine first 4 ingredients in a small bowl; stir until blended.
3. Cut 2 (15 x 24-inch) pieces of parchment paper. Fold in half crosswise. Draw a large heart half on each piece, with the fold of the paper along the center of the heart. Cut out the heart, and open. Sprinkle both sides of fillets with salt and pepper. Place one fillet near fold of each parchment heart. Top each fillet with half the vegetables and half the butter mixture. Start at the top of the heart and fold edges of parchment, sealing edges with narrow folds. Twist the end tip to secure tightly. Place packets on a baking sheet. Bake at 450° for 15 minutes. Place on plates; cut open. Serve immediately.
Sustainable Choice: If arctic char is not available from your fishmonger, substitute frozen wild Alaskan salmon.