Prepare ahead

The sauce can be made several hours in advance.

1. To make the sauce: Cook the gooseberries with 2 tbsp water in a saucepan over medium heat for 4–5 minutes, until tender. Purèe in a food processor, then add the butter, sugar, and nutmeg, and season with salt and pepper. Keep warm.

2. Cut the heads off the herring and slit them open along the belly right down to the tail. Open the fish out flat and place them skin side up on a cutting board. Bone each fish into a "butterfly" by pressing firmly all along the backbone with the heel of your palm until it is completely flat, then turn it over and pull away the backbone, snipping it off at the tail end with scissors. Remove any small bones left behind in the fish with a pair of tweezers. Alternatively, fillet the herrings.

3. Spread the oatmeal on a large plate and season generously with salt and pepper. Coat the herrings in the oatmeal, pressing it well onto the fish.

4. Position a broiler rack 6in (15cm) from the source of heat and preheat the broiler. Arrange the herring in a broiler pan. Broil for 6–8 minutes, turning once, until the flesh looks opaque when flaked. Serve with the gooseberry sauce.