Prepare all ingredients: chop spring onions, cut haddock into chunks, peel prawns, measure butter, Dijon mustard, chicken stock, crème fraîche, chives, and lemon juice
Set out serving bowls and spoons for final plating
Place a medium saucepan over medium heat, add butter, allow to melt gently
Add chopped spring onions to the saucepan, sauté until softened, about 2 minutes
In a separate small bowl, whisk Dijon mustard into chicken stock until fully combined
Pour the mustard-infused stock into the saucepan with spring onions, stir to combine, bring to a gentle simmer
Place smoked haddock chunks into the simmering liquid, cover, poach gently for 3-4 minutes until fish is nearly opaque
Add raw, peeled prawns to the saucepan alongside the haddock, continue to simmer gently for 2-3 minutes until prawns turn pink and just cooked through
In a small bowl, mix crème fraîche with chopped chives and a squeeze of lemon juice to form a fresh, tangy topping (parallel task)
Taste the stew, adjust seasoning if desired (but remember smoked haddock adds salt)
Remove pan from heat, gently stir in half the crème fraîche mixture to enrich the stew
Ladle stew into warm serving bowls
Top each bowl with a generous dollop of the reserved crème fraîche-chive-lemon mixture
Scatter extra chopped chives over the stew for garnish
Serve immediately with lemon wedges on the side, if desired