Remove the skin from the herring. Peel the onion and slice it using a mandolin. Place the fish in a vacuum bag with the liquid, the onion and the dill. Seal the bag and marinate 40 minutes. Drain the fish, cut it into 2 cm slices and season with lemon juice. If you don’t have access to a vacuum machine you can marinate the fish for about 2 hours in a regular bowl instead.
Boil the potatoes in salted water. Brown the butter, add the anchovies and let the fish melt into the butter. Add the milk and bring to a boil. Press the potato through a sieve and and combine with the butter mixture to obtain a smooth cream. Season with salt and pour the cream into a siphon. Load with one gas capsule and keep in a bain marie at 75°C for 20 minutes. If you don’t have access to a siphon you can serve the foam as a creamy sauce instead.
Mix the wet ingredients in one bowl and the dry ingredients in another bowl. Combine the two and mix well. Spread the batter onto a silicone sheet and place another one on top for extra weight. Bake for 20 mins in an oven at 150°C. Remove the top silicone sheet and bake another 5 mins. Allow to cool and break into pieces.
Split the pickling onions lengthwise and steam 30 seconds. Peel them and place them in the liquid.
Peel the shallots and slice them thinly on a mandolin. Divide the slices into rings, toss in corn starch and deep fry until crispy.
Brown the butter and allow it to cool. Boil the potatoes just before serving and salt it lightly. Pluck the herbs and place them in cold water.