Line a 24cm springform baking tin, with greased kitchen foil
Cook the potatoes in a large pan of boiling, salted water for 3-4 minutes, until just tender, drain in a colander; it doesn’t matter if some slices break but do try to keep most whole
Heat the oil in a large frying pan over a medium heat and saute the spring onions for 2-3 minutes; add the courgettes, turn them in the oil and sprinkle with a little salt; let them cook for about 6-8 minutes, stirring occasionally; do not let them brown; remove from the pan and set aside to cool on kitchen paper; add them to the eggs together with the herbs and some seasoning
Preheat the oven to 190C/Gas5; use a third of the potatoes to make a layer in the bottom of the baking tin, then spread over half of the tomato sauce, then half the egg and courgette mixture, then half the feta; repeat the layering process, finishing with a layer of potatoes; drizzle over a little oil, then cover with foil and push down to make sure the cake is compact; place on a rimmed baking sheet and bake for 40 minutes
Uncover, turn the heat up to 200C/Gas6 and cook for another 30 minutes or so, until browned and bubbling; let it stand for 10 minutes, or so before turning out and cutting into slices
6 servings