This glorious cake is my favourite picnic food – tinned mackerel, potato salad and boiled eggs – all rolled into one. It’s best made a day ahead, so it has plenty of time to set in the fridge, but four hours should do the trick, if need be.
1hr 20 min
750g small to medium new potatoes
Flaked sea salt and black pepper
1 tbsp dijon mustard
240g tinned mackerel in olive oil, drained
4 spring onions, finely sliced
200g pitted kalamata olives, roughly chopped
300g cherry tomatoes, halved
60ml olive oil
3 tbsp harissa, or less, depending on your taste for spice
2 tsp maple syrup
For the parsley salsa
1½ tbsp flat-leaf parsley, finely chopped
1 lemon – zest finely grated, to get 1 tsp; and juiced, to get 1½ tbsp
1 garlic clove, peeled and crushed
2 tbsp oil
1 big pinch flaked salt and black pepper
1. Heat the oven to 200C/390F/gas 6. Put the potatoes in a medium saucepan of cold, well-salted water. Bring to a simmer, then cook for 25 minutes, until the potatoes are soft but still hold their shape. Drain and set aside to cool.
2. While the potatoes are cooking, half-fill a large saucepan with water, bring to a boil, turn down the heat to medium-high so the water is boiling gently, then lower in five eggs and cook for six minutes. Drain, leave the eggs under the cold tap for a couple of minutes, to stop them cooking any more, then peel and set aside. Whisk the mayonnaise with the remaining two eggs and the mustard.
3. Line the base and sides of a 20cm cake tin with greaseproof paper. Lay out the potatoes on a chopping board and squash them flat with a fork or potato masher, so they’re about 1.5cm thick. Put half the squashed potatoes in the base of the tin, pressing them very firmly together to form a compact layer. Sprinkle with a little flaked salt and pepper, then top with half the mackerel, half the spring onions and half the olives. Pour half the mayonnaise mix evenly over the top.
4. Cut the soft-boiled eggs in half lengthways, and lay them yolk side up on top of the spring onions.
5. Top with a final layer each of mackerel, spring onions and olives, in that order, then lay the remaining squashed potatoes on top, pressing them down to form a compact layer. Sprinkle with salt and pepper, then pour over the remaining mayonnaise mixture and press the whole thing down very well to compact it.
6. Toss the tomatoes with the harissa, maple syrup and two tablespoons of oil, and scatter evenly on top of the potato layer.
7. Place a tray under the cake tin to catch any oil, then bake for 35-40 minutes, until the tomatoes have softened and are slightly charred. Refrigerate until cool and set, for at least four hours, and preferably overnight.
8. Mix the parsley salsa ingredients, remove the cake from the tin and drizzle evenly with parsley salsa.