Haddock, leek and mustard gratin

This recipe was inspired from Marcus Waring’s at Home cook book, this version is made with frozen haddock.  It’s absolutley delicious, one that my family really enjoys and they are not great fish eaters!


  • 4 frozen haddock fillets
  • 25g butter
  • 4 large leeks – whites only, thinly sliced
  • 1 tsp dried thyme
  • 150ml vegetable stock
  • Salt and pepper

For the crumb

  • 80g panko breadcrumbs
  • 20g grated cheddar cheese
  • 1 tsp dried thyme

For the sauce

  • 60g salted butter
  • 60g plain flour
  • 600ml semi-skimmed milk
  • 120g cheddar cheese, grated
  • 1 tbsp wholegrain mustard
  • 1 tbsp english mustard
  • 2 tsp worcester sauce


  1. Preheat the oven to 180ºc / Gas 4.
  2. Place the haddock fillets on the tray and bake in the oven for 15mins until partially cooked.  Set aside to cool slightly.
  3. Whilst the haddock is cooking, make the crumb.  Mix all the crumb ingredients together and set aside.
  4. Now make the sauce, melt the butter in a saucepan and when it starts bubbling stir in the flour.  Top tip: by using a large balloon hand whisk, you will find that you will not have any lumps.
  5. Cook for 30seconds then gradually start adding the milk, stiring constantly so that the sauce doesn’t catch on the bottom of the pan. Bring to a simmer and cook for 2mins, then stir through the cheese until melted. Add both the mustards, worcester sauce, season and set aside.
  6. Once the fish is cool enough to handle, break up into a shallow dish.
  7. Increase the oven to 220ºc/gas 7.
  8. Now cook the leeks, melt the remaining 25g butter in a frying pan, add the leeks and cook for 5mins until starting to soften.  Add the thyme and stock and cook for around 5mins.  Once cooked, gently fold into the haddock. 
  9. Spoon over the cheese and mustard sauce, scatter over the crumbs and bake in the oven for 15mins until the crumb is golden and the sauce is bubbling.  Serve with peas or green veg.