Peel and cut the celeriac into chunks. Trim the medium leeks.
- 1 Place the celeriac, garlic, bay leaves and a pinch of salt in a saucepan, and add milk until just covered.
- 2 Bring the mixture to a boil, then reduce the heat and simmer gently for 15-20 mins, until the celeriac is fork tender.
- 3 While the celeriac is cooking, prepare your leeks.
- 4 Turn your grill onto its highest setting.
- 5 Cut leeks in halves or thirds widthways, then cut in half lengthways.
- 6 Spread the leeks cut-side up on a baking tray, then drizzle 2 tbsps olive oil over the top.
- 7 Sprinkle salt and pepper over the top to season, then place under the grill for 10-15 mins, until cooked through and charred on top.
- 8 Remove from the oven and set aside.
- 9 Take the celeriac off the heat, drain the milk (reserving a few tablespoons worth) and carefully remove the bay leaves.
- 10 Then, using a stick blender, whizz the celeriac to a puree, adding a few splashes of milk as you go (until you have your desired consistency).
- 11 Add the mustard and season with salt and pepper as necessary, then whizz again until combined.
- 12 Cover and set aside on a low heat to keep warm.
- 13 Finally, prepare your fish and sauce.
- 14 Heat up 1 tbsp olive oil in a large saucepan over medium heat.
- 15 Season the haddock fillets, and pan fry according to pack instructions.
- 16 While they are cooking, heat up parsley sauce according to instructions.
- 17 When the fish is done, assemble the dish.
- 18 Split the mash and leeks evenly between four plates, and top with haddock fillets.
- 19 Pour a spoonful of sauce over each fillet, and serve immediately.