Push a clove into the skin of each onion. Place in a pot or large skillet, add milk, turn stove onto medium high heat.

When milk is barely simmering, add fish - don't worry if it's not entirely covered, it can be turned / moved around.

Poach fish for 7 minutes, then use a slotted spoon to transfer fish straight into a medium baking dish (Note 8).

Flake into chunks using forks. Remove bones if you see any.

Use slotted spoon to remove onion and cloves from milk, discard. RESERVE milk.

Preheat oven to 180C/350F. Boil water for potatoes.

Melt butter in a large, deep skillet or pot over medium high heat. Add onion and garlic, cook for 1 minute. Then add celery and carrot, cook for 5 minutes until carrot is soft.

Turn heat down to medium low. Add flour, mix in - it will look gluey.

Add half the milk and quickly start mixing. Once incorporated, the mixture will thicken quickly. Add remaining milk and stir. (Video helpful here)

Turn heat up to medium and keep stirring until the mixture thickens to the consistency of honey - about 3 minutes. (Note 7)

Take it off the heat, stir through tarragon and parsley. Adjust salt and pepper to taste.

Scatter top of flaked fish with peas, then pour over the Sauce. GENTLY stir through (don't want fish to turn into mush!).*

Smooth top, then nestle egg in all over the pie.

Bring a large pot of water to the boil. Add potatoes and cook for 15 minutes or until soft. (Do this while making the Sauce).

Drain potato, add butter, milk, salt and pepper. Mash until creamy - add more milk if required.

Immediately dollop then spread onto pie (cold mash = hard to spread).

Use fork to draw squiggles on surface (rough surface = better golden bits).

Drizzle surface with melted butter, sprinkle with parmesan.

Bake for 35 minutes or until top is deep golden.

Stand for 5 minutes before serving, garnished with parsley if desired. See notes for reheating and make ahead.