Trout and Smoked Haddock Fish Pie

Ingredients

• 1kg floury potatoes (e.g. King Edward or Maris Piper), peeled
• Knob of butter
• Splash of milk
• Salt and pepper
• Handful grated cheddar cheese, if liked
• 30g butter
• 30g plain flour
• 5 spring onions, sliced
• 265g ChalkStream trout fillets, skinned and cut into chunks
• 250g smoked haddock, skinned and cut into chunks
• 400ml milk
• 1 tsp mustard