Fish Pie with Mashed Potatoes and Vegetables

Like a fish shepherd's pie; the zucchini helps thicken the filling, but disappears in the sauce.

1½ lbs russet potatoes, peeled, cut into 2" pieces (~ 3 medium)
sea salt
3 Tbsp. butter, divided + 3 Tbsp. melted
1 leek, white and pale-green parts only, thinly sliced into rounds
black pepper, freshly ground
¾ cup heavy cream, divided
1 medium zucchini, grated
1 clove garlic, finely chopped
⅓ cup brandy
¾ cup canned crushed tomatoes
½ lb firm white fish fillets, such as cod, haddock, or halibut, skinless
½ lb salmon or arctic char fillets, skinless
4 oz medium shrimp, peeled, deveined, halved lengthwise
2 oz smoked trout, flaked
1 Tbsp. fresh dill, chopped

Preheat oven to 350°F (180°C/160°C fan, Gas Mark 4).

Cook potatoes in a large pot of boiling salted water until tender, 15-20 minutes. Drain; return to pot.

Melt 1 Tbsp. butter in a large skillet over medium-high heat. Add leek, season with salt and pepper; cook, stirring occasionally, until soft, about 5 minutes. Add leek to potatoes along with ½ cup cream and 3 Tbsp. melted butter. Season with salt and pepper and mash to desired texture.

Melt remaining 2 Tbsp. butter in a large skillet over medium heat. Add zucchini and cook, stirring often, until browned and beginning to stick to skillet, 8-10 minutes. Add garlic, season with salt and pepper; cook until fragrant, about 1 minute. Add brandy and cook, stirring, until mixture is thickened, about 2 minutes. Add tomatoes and bring to a simmer. Add white fish and salmon and cook, stirring gently, until fish is opaque around edges, about 1 minute. Stir in shrimp and trout and cook until shrimp are opaque. Remove from heat, stir in dill and remaining ¼ cup cream, and season with salt and pepper.

Transfer filling to a 2 qt baking dish and top with mashed potatoes, making decorative swirls with a large spoon or fork. Place on a baking sheet and bake pie until mashed potatoes are golden brown and center is hot, 40-45 minutes.