Fish: Using frozen fish is fine, but make sure to fully thaw it first.
Cheese: For a lighter option, consider using low-fat cheddar.
Sauce Thickness: If the sauce feels too thick, add a splash of milk to thin it out; too thin, and a little more flour can help thicken it.
Cheese Alternatives: If you're not a fan of cheddar, Gruyère or Parmesan also work well as a cheesy topping.
Oven Temperatures: Ovens can vary. Keep an eye on the pie during the last 10 minutes of baking to avoid over-browning.
Gluten-Free: To make this dish gluten-free, use gluten-free flour for the roux and ensure all other ingredients are gluten-free.
Make-Ahead: The fish filling can be prepared a day in advance and stored in the fridge, covered. Assemble and bake the next day for an easy meal prep.