Smörgåskaviar

Method

1. Lay the roe on a board and slit the membrane lengthways with the tip of a small knife. Scrape 110 g of the smoked cod roe away from the skin with the back of the blade and drop it into a small bowl; discard the membrane, which is tough and stringy.
2. Mash the roe with a fork for a minute or two until the grains break down into a coarse, even paste. Work in 1 tbsp of tomato purée and 1 tsp of caster sugar — the purée gives the pink-red colour and the sugar the characteristic sweet-salt balance.
3. Add 1 tbsp of rapeseed oil a few drops at a time, beating hard with the fork or a small whisk after each addition so it emulsifies rather than splits. The paste should turn thick, smooth and glossy and hold a ridge.