Freezer Lemon Dill Fish Pie Flaky fish beneath a bright creamy potato lid
“Cold thick sauce protects fish from overcooking during assembly.”
Published by MommyCooking.org · Published September 30, 2026
This is a make-two-eat-one dish: it assembles in half an hour, bakes in another forty, and the second dish goes straight into the freezer for a week when nobody wants to cook. White fish is cheaper than it looks when it is buried under a potato lid, and eight servings come out of one pan.
The sauce must be completely cold before the fish and potato meet it. Warm sauce starts cooking the fish during assembly, which is how you end up with dry, chalky pieces after the bake, and it soaks upward into the potato instead of staying put. Cooling also thickens it enough to hold the peas in place.
🐟 The promise: A whole tray of fish pie for eight, assembled cold in under half an hour and then either baked straight away or wrapped for a night when nothing is planned.
🐟 Everything you need, all in one look🧂 Ingredient notes & easy swaps
Cod is the default because its thick flakes survive baking, but haddock, pollock or any firm white fish behaves the same way. Frozen peas go in straight from the bag and hold their color better than fresh ones would. Mashed potato needs to be stiff; a loose, buttery mash slides off the sauce instead of sealing it.
Three tablespoons of flour to three cups of milk is a deliberately loose roux. The sauce should coat a spoon and go no further, because the cod and the peas both release water into it in the oven.
Dill loses its scent under long heat. A second small handful stirred over the pie as it leaves the oven does more for the lemon than doubling the amount stirred into the sauce.
🍳 What you actually need (equipment)
a medium saucepan, a whisk for the roux and the milk, a 9-by-13-inch baking dish, a fork for roughing up the potato peaks, and an instant-read thermometer
Melt 3 tbsp (42 g) butter in a saucepan, whisk in 3 tbsp (24 g) flour, and cook 2 minutes over medium heat. The paste should smell faintly like toast and stay blond rather than browning.
Cook the butter-flour roux
Pour in 3 cups (720 ml) milk a splash at a time, whisking out lumps before adding more. Simmer 5 minutes until the sauce coats the back of a spoon and holds a line drawn with your finger.
Whisk the milk sauce
Stir in ¼ cup (15 g) dill, 1 tbsp (15 ml) lemon juice, and ¼ tsp (1.5 g) kosher salt, then cool the sauce completely. Cold sauce stays put around the fish instead of soaking into the potato lid.
Season and cool the sauce
Pat 1½ lb (680 g) cod cut in 1-inch pieces dry with paper towels and scatter them across a 9-by-13-inch baking dish with 2 cups (280 g) peas. Leave small gaps so the sauce can settle between the pieces.
Lay fish and peas
Spoon the cold sauce evenly over and around the fish, then spread 4 cups (840 g) mashed potatoes to every edge so no sauce can bubble up the sides. Rough the surface with a fork to make peaks that brown.
Top with mashed potatoes
Bake at 400°F (205°C) for 32 to 38 minutes, until the potato peaks turn gold and the sauce bubbles at the center. The cod should flake apart at a fork and register 145°F (63°C).
Bake until the fish flakes
✅ How to know it's done
The fish is opaque through, the sauce simmers in the middle, and the potato ridges are crisp. If the potato peaks are gold well before the center bubbles, the dish went in colder than the method assumes. Cover it loosely with foil and keep baking until a piece of cod from the middle reads 145°F (63°C).
💡 Practical tips (and what not to do)
Keep the roux blond. Two minutes is enough to lose the raw flour taste, and browning it dulls the lemon and dill you add later.
Add milk in splashes. Pouring it all in at once guarantees lumps that no amount of whisking will fully break up.
Pat the fish dry. Surface water thins the sauce around each piece and leaves a watery layer at the bottom of the dish.
Seal to every edge. Potato spread right to the rim stops the sauce boiling up the sides and burning onto the dish.
Rough up the top. Fork ridges give you the browned peaks that make the difference between a pie and a casserole.
Budget: use frozen white fish fillets thawed and patted very dry, which cost considerably less than fresh. Lighter: make the mash with broth instead of butter and use a lower-fat milk in the sauce. Kids: cut the fish into smaller pieces and hold the dill back to a tablespoon. Extra flavor: add grated lemon zest to the potato, or a spoonful of grainy mustard to the sauce.
💛✨ Flavor boost
Steep a wide strip of lemon peel in the milk as it warms, then lift it out before the sauce thickens.
🥔 What Goes Well With It
Wilted spinach with nutmeg, cooked while the pie rests.
Pickled cucumber or a spoonful of capers, which cut the creamy sauce.
Bread for the sauce left at the bottom of the dish.
📦 Storage & Freezer Notes
Refrigerate leftovers up to two days; fish in sauce does not hold as long as a meat dish would.
Warm it covered at 350°F (175°C) for about twenty minutes, taking the middle to 165°F (74°C) with the sauce bubbling.
Freeze the pie unbaked and well wrapped for up to three months, then bake from frozen with an extra twenty-five minutes.
Make the sauce the evening before and refrigerate it. It is the one component that cannot be hurried, and a properly cold sauce spreads more neatly than a freshly cooled one.
Let a baked pie stand ten minutes before serving, or the sauce runs across the plate and away from the potato.
🧒 Serving Ideas for Kids
Serve from the middle of the dish, where the potato is soft, rather than the browned corners.
Check each spoonful for bones before it goes onto a small plate, even with fillets that were sold boneless.
Let the portion sit for five minutes; a sauced bake holds heat far longer than the surface suggests.
❓ Quick answers
Can I assemble this ahead and bake later?
Yes, and that is the point of it. Assemble completely, cover, and refrigerate up to a day or freeze for months. From cold out of the refrigerator, add about ten minutes to the bake time.
Do I need to thaw frozen fish first?
For this, yes. Frozen pieces release water directly into the sauce and thin it badly. Thaw them overnight in the refrigerator and pat them thoroughly dry before they go into the dish.
Can I use instant mashed potato?
It works, and it needs to be made stiffer than the package suggests. Use about three-quarters of the liquid called for, or the lid will be too loose to spread and will sink into the sauce.
How do I know the fish is cooked through?
The pieces should be opaque and flake apart under gentle pressure at 145°F (63°C). Since they are buried, use the temperature rather than looking, and check a piece near the center of the dish.
🥗 Nutrition, roughly: about 455 calories per serving. Estimates only; brands, cuts and portion sizes change the numbers.
Published by MommyCooking.org. This AI-assisted recipe passed automated checks for page consistency and required image files. A real-kitchen test has not been documented for this dish. The food images are AI-generated illustrations, not photographs of a cooking session. Cooking temperatures should be checked with a food thermometer; nutrition figures are estimates. How we make recipes · Report a problem with this recipe
