Creamy Fish Pie Recipe - Easy & Cheesy Mash Topping

Picture this: a bubbling, golden-brown crust of cheesy mashed potatoes crowning a rich, creamy seafood filling brimming with tender fish and savory veggies. That, my friends, is the magic of a classic British-style fish pie recipe. It’s the ultimate cozy comfort food, perfect for chilly evenings or a satisfying family dinner.
Now, let's clear something up right away. When we talk about "fish pie" in the British tradition, we're not talking about a pie with a flaky pastry crust (though you absolutely can adapt this incredible filling for one—we’ll show you how!). This is a hearty casserole where a luscious, often cheesy, mashed potato topping reigns supreme. It’s a fantastic meal for busy weeknights, brilliant for meal prep, and it even freezes beautifully, making it a true kitchen hero. Get ready to dive into a dish that’s easy to love and even easier to make!

Ingredients

• For the Mashed Potato Topping:
• 2 lbs (about 4 medium) Russet or Yukon Gold potatoes, peeled and cut into 1-inch chunks
• 4 tablespoons unsalted butter
• ¼ cup whole milk or half-and-half, warmed
• ½ teaspoon salt, plus more to taste
• ¼ teaspoon black pepper, plus more to taste
• ½ cup shredded sharp cheddar cheese (optional, but highly recommended!)
• For the Fish Filling:
• 1 tablespoon olive oil or unsalted butter
• 1 medium yellow onion, finely chopped
• 2 cloves garlic, minced
• 1 stalk celery, finely chopped (optional)
• 1 carrot, finely chopped (optional)
• 1 ½ lbs mixed fish fillets (see "Fish Selection Guide" below for US-friendly options)
• Mild white fish options: Cod, Haddock, Hake, Tilapia, Pollock
• Rich fish options: Salmon (skinless, boneless)
• Optional smoked element: Smoked Haddock (if available). If not, add a pinch of smoked paprika to the sauce.
• 4 oz raw shrimp (peeled, deveined, tails off), cut into 1-inch pieces (optional)
• ½ cup frozen peas, corn, or chopped fresh spinach (optional add-ins)
• For the Creamy Sauce:
• 4 tablespoons unsalted butter
• 4 tablespoons all-purpose flour
• 2 cups whole milk (reserved from poaching fish, if applicable)
• 1 cup heavy cream (or additional whole milk)
• 1 tablespoon Dijon mustard
• 1 tablespoon fresh lemon juice
• 2 tablespoons fresh dill or parsley, chopped (or 1 teaspoon dried mixed herbs)
• Salt and black pepper to taste

Directions

1. Prep + Preheat
   1. Preheat your oven to 400°F (200°C).
   2. Lightly grease a 9x13-inch (3-quart) baking dish. A deeper dish works best to hold all that delicious filling and a generous potato topping!
2. Cook and Mash the Potatoes
   1. Place the peeled and chopped potatoes in a large pot and cover with cold, salted water by about an inch. Bring to a boil, then reduce heat and simmer until fork-tender, about 15-20 minutes.
   2. Drain the potatoes thoroughly. Return them to the hot, empty pot and let them sit for a minute or two over very low heat (or just off the heat) to steam off any excess moisture. This is key for fluffy, dry mash that browns beautifully!
   3. Add the butter, warmed milk/half-and-half, salt, and pepper to the potatoes. Mash until smooth and creamy. Don't overmix!
   4. Stir in the shredded cheddar cheese (if using) until just combined. Taste and adjust seasoning.
3. Build the “Milk Broth” (Quick-Poach Method)
   1. In a large, deep skillet or pot, gently combine the 2 cups of whole milk (for the sauce) with the fish fillets. If using smoked haddock, add it now.
   2. Bring the milk to a very gentle simmer over medium-low heat. Do not boil hard; this can toughen the fish.
   3. Poach the fish gently for 5-7 minutes, or until it's just cooked through and flakes easily.
   4. Carefully remove the fish from the milk using a slotted spoon and set aside to cool slightly. Reserve the milk! This flavorful milk will be the base for your creamy sauce.
   5. Once cool enough to handle, flake the fish into large chunks, checking carefully for any bones or skin.
4. Make the Sauce
   1. In the same skillet (no need to clean), melt the 4 tablespoons of butter over medium heat.
   2. Add the chopped onion, garlic, celery, and carrot (if using). Sauté for 5-7 minutes until softened and fragrant.
   3. Sprinkle in the 4 tablespoons of all-purpose flour. Cook, stirring constantly, for 1-2 minutes to cook out the raw flour taste (this is your roux!).
   4. Gradually whisk in the reserved milk from poaching the fish, a little at a time, ensuring no lumps form. Continue whisking until the sauce thickens to your desired consistency – it should be thick enough to coat the back of a spoon.
   5. Stir in the heavy cream (or extra milk), Dijon mustard, and lemon juice. Season generously with salt and pepper.
   6. Gently fold in the flaked fish, shrimp (if using), and any optional veggies (peas, corn, spinach). Taste the filling and adjust seasoning as needed.
5. Assemble
   1. Pour the creamy fish filling into your prepared baking dish, spreading it evenly.
   2. Spoon the mashed potato topping over the fish filling. Spread it gently to the edges, sealing in the filling. For a crispier top, create fork ridges across the surface.
6. Bake + Brown
   1. Bake for 20-25 minutes, or until the filling is bubbling around the edges and the mashed potato topping is lightly golden.
   2. For an extra golden and crispy top, you can carefully broil for the last 2-4 minutes. Watch it closely to prevent burning!
7. Rest + Serve
   1. Remove the pie from the oven and let it rest for 5-10 minutes before serving. This allows the filling to set slightly, preventing it from being too runny.
   2. Serve hot with a simple side of fresh greens, steamed peas, or a crisp salad.