Makes 2 × 500g jars
To sterilise the jars, preheat the oven to 160°C fan/180ºC/Gas 4. Wash the jars and lids really well and put them on a baking tray in the oven for 10 minutes.
Put a clean cloth on the kitchen table and lay out the fillets in close rows, skin-side down. Evenly scatter over the salt and leave them for 1½ hours.
To make the marinade, crush the juniper berries and coriander seeds a little under a knife, as this will help them release their taste. Tip all the spices into a medium pan and warm them over a low heat until their smell comes to the nose. Do not burn them. Pour in the vinegar and sugar. Scrumple the bay leaves to help them release their aroma, and then add them to the pan. Continue to simmer gently to melt the sugar as you prepare the carrots.
If you like, use a canelle knife to cut four equally spaced grooves down the entire length of each carrot. (This is not obligatory, but will give a pretty flower pattern to each sliced piece.) Slice them as close to paper-thin as you can and add to the pot with the onion. Bring it all up to the boil, then reduce the heat and simmer gently for 5 minutes. Leave to cool completely. If the liquid is applied to the fish hot, they will cook rather pickle and all hands would be lost.
When their time is up, put the herrings in a colander and rinse well under cold water. Pat the fillets dry with kitchen paper. Cut each fillet in half at a diagonal angle. Sprinkle some of the marinade into the base of the two sterilised jars and scatter with a few pieces of the fish. It’s nice if the silvery sides press against the glass, as this is what you will see when opening the fridge or when the jar is placed on the table. Add a little onion and carrot. Continue layering the jars, fairly dividing the bay leaves between them, until the top of each jar is reached. Make sure that the pickling liquor completely covers the fish and goes to just under the brim of each jar.
Cover tightly and chill in the fridge for at least two days before serving. Eat them before and they will not have had time to soften and mature; open a tin of pâté instead. They will store well in the fridge for 1 month, but should be eaten within a week once opened. (This is why it is better to make them in smaller jars rather than a single big one.)
Serve with good rye bread, cold butter and hot horseradish, making sure each loaded morsel is quivering with the onion and carrot.