Halibut Foil Packs with Chile Butter

Real Talk: Halibut is a firm-fleshed, flaky white fish. If you can’t find it, use something similar, like cod, hake, or salmon (not white, but texturally similar). If you use a thinner fish (like flounder), you’ll have to reduce the cook time; check it after 6–7 minutes.

Pat halibut dry with paper towels; season with salt and pepper. Chill, uncovered, 30 minutes.

Meanwhile, preheat oven to 450°. Cook bok choy in a large pot of boiling salted water until bright green but still very firm, about 1 minute. Transfer to a paper towel-lined rimmed baking sheet to drain. Cook onion in same pot of boiling salted water until heated through, about 30 seconds; transfer to same sheet.

Mix garlic, butter, chile powder, mustard, vinegar, and ½ tsp. salt in a small bowl until combined.

Lay out four 12" sheets of foil. Divide bok choy among sheets; top each with a piece of halibut and a schmear of ancho butter. Top with onions. Fold edges up and over to create packets; pinch seams closed. Transfer packets to a rimmed baking sheet and bake until fish has cooked through (remove 1 packet, carefully unwrap, then press fish with your finger; it should easily flake apart), 8–10 minutes. Remove from oven and let sit unopened 2 minutes to steam.

Divide fish and vegetables among plates, then pour juices over.