Mix together milk and cream cheese in a bowl.
Combine haddock, peas, corn, salt and black pepper in another bowl.
Put the haddock mixture in the Instant Pot and layer with milk mixture.
Set the Instant Pot to “Manual” mode for 5 minutes at high pressure.
Release the pressure naturally and dish out the pie.
Preheat the oven to 140oF and mix together breadcrumbs and Cheddar cheese in a bowl.
Sprinkle the top of the pie with Cheddar mixture and bake for about 10 minutes.
Remove from oven and serve hot.