To steam halibut en papillotte, lay out 2 pieces of parchment paper approximately 13 x 17 inches. In center of bottom half of each sheet, smear 1 tsp butter as base for halibut. Place each halibut piece on top and season with salt, pepper, and paprika. Cut lemon slices in half and lay them over top of halibut. Seal parchment packages by folding top of piece toward bottom and rolling edges closed. Place on baking sheet and cook for 17 minutes. Remove from oven and allow to stand in parchment packages for 2 minutes.