Pickled Mustard Seeds

• Pop all of the of ingredients in a small saucepan and bring to a slow boil. Stir several times, making sure the sugar has dissolved. Reduce the heat and simmer for about 5-8 minutes. Remove from the heat and allow to cool to room temperature. Transfer to a sterilised jar and store in the fridge.
• Begin with melting a knob of butter in a saucepan and then add the garlic. Follow with the celeriac and 50ml water a large pinch of salt. Cut a round piece of baking paper the same size as the pan and use to cover the celeriac (cartouch). Cook gently for 15-20 minutes, stirring regularly, until the celeriac is very soft and starting to collapse, you may need to add a splash of water. Blitz in a high speed blender, then pour back into the saucepan. Simmer to drive off any excess water that may still remain in the puree. Season if needed and add the milk and creme fraiche. Set aside.
• Now to make the sauce. Gently saute the shallot in a little butter for a few minutes to soften before adding the white wine. Let it bubble gently for a minute or so and then pour in the fish stock. Now add the Dijon mustard and creme fraiche. Whisk it all together, season and then take off the heat and set aside while you sauté the hake. Brush the fillets first with olive oil, season. Sauté in a medium-hot frying pan for 3-4 minutes each side, depending on the thickness.
• In the meantime, gently simmer the leeks in water for 2-3 minutes or just cooked through. Gently heat the mustard sauce through, add the parsley.
• Spoon the celeriac puree onto the plate, top with the fish and spoon the sauce and leeks onto each plate. Scatter with pickled mustard seeds. Serve immediately.