The fish fillets should fit rather snugly in the pot with enough room for some shrimp to slip between the crevices. The braising liquid is a nifty mixture of chicken broth, white wine, and Thai green curry paste--available in most supermarkets these days. Fresh, never frozen, halibut is best; if you can't find it, sub another meaty white fish or Alaskan salmon.
1. Heat a large skillet over medium-high heat. Add oil and butter to pan; swirl until butter melts. Add leeks; sauté 3 minutes, stirring occasionally. Add garlic and carrots; sauté 3 minutes, stirring constantly. Remove from heat. Sprinkle salt evenly over both sides of fillets; arrange fillets and shrimp in a single layer on top of carrot mixture.
2. Combine broth, wine, and curry paste in a small bowl, stirring with a whisk. Add curry mixture to pan with fish; bring to a boil. Cover, reduce heat, and simmer 10 minutes or until desired degree of doneness. Place 1 fillet in each of 4 shallow soup bowls; divide shrimp, vegetables, and broth evenly among servings. Sprinkle each serving with 1 1/2 teaspoons mint.