Step 1

Boil potatoes: Bring a large pot of water to a boil and add the cubed potatoes. Cook for for 15 to 20 minutes or until the potatoes are fork tender. Drain.

Step 2

Mash the potatoes: Place the drained potatoes back in the pot or a bowl, add the 3 tbsp of butter, the ⅔ cup of milk and ½ tsp of salt. Using a potato masher, mash the potatoes until creamy. Set aside.

Step 3

Prep the oven: Preheat the oven to 350°F.

Step 4

Cook the veggies: In a large skillet melt the butter over medium heat. Add the green onions, carrots and garlic and cook for 2 minutes. Sprinkle the flour over the veggies and stir. Cook for 2 more minutes to remove the raw flour taste.

Step 5

Add the rest of the ingredients: Slowly pour the 2 cups of milk to the skillet and whisk until smooth and thickened, about 3 minutes. Add 1 cup of the cheddar cheese, dijon mustard and dill to the sauce and stir until the cheese melts. Add in the fish, gently stir and cook for 1 to 2 minutes. Stir in the frozen peas and season with the salt and pepper.

Step 6

Assemble the pie: Pour the filling in a 9x13-inch ovenproof dish and top with the mashed potatoes. Smooth with a spoon then take a fork and rough up the top a bit. Sprinkle with remaining cup of cheddar cheese.

Step 7

Bake the pie: Place the casserole dish on a baking pan and transfer to the oven. Bake for 30 to 35 minutes or until the top starts to get golden.

Step 8

Ready to serve: Garnish with more dill or parsley and serve.