Slightly adapted from the September/October 2011 issue of Ingredient, a magazine for children, where it was originally published as Catch of the Day Pie. Makes 4 individual pies, or a single pie that serves 4.
12 oz cod fillets (or use half salmon fillets), skin removed
1-1/2 cups skim milk
1/4 cup chopped leeks
6 oz raw large shrimp (31-40 size) or langoustines, peeled and deveined
3 Tbsp butter
2 Tbsp all-purpose flour
1/2 cup peas
1/2 cup corn kernels
1 Tbsp minced parsley
4 Tbsp lemon juice
1/2 cup grated cheddar cheese
1/2 tsp kosher salt
1/2 tsp fresh black pepper
2 cups mashed potatoes (2 large Idaho potatoes + 2 Tbsp butter + 1/2 cup milk)
Preheat oven to 350°F. Place 4 individual baking dishes on a rimmed baking sheet, and set aside.
Place the cod in a baking dish with the milk and chopped leeks. Cover the dish tightly with foil, and bake for 15 minutes. With a slotted spoon, remove the fish and leeks to a bowl, and reserve the milk. When the fish has cooled for a few minutes, break it into chunks.
In a sauce pan, melt the butter over low heat. When it bubbles, stir in the flour with a wooden spoon, and cook for 2 minutes. Slowly add the reserved milk, and cook, stirring frequently, until the mixture thickens to the consistency of gravy. Add the fish and leeks, shrimp or langoustines, peas, corn, parsley, lemon juice, cheese, salt and pepper, and cook for 4-5 minutes until the shrimp are just cooked (not overcooked). Divide the mixture among the four prepared dishes.
Divide the mashed potatoes equally among the four dishes. To make a fancy topping, thin the potatoes with enough additional milk so you can pipe them through a pastry bag fitted with a star tip.
Bake for 30 minutes until the tops are starting to brown and you can see the filling bubbling a bit along the edges of the baking dishes.