Preheat the oven to gas 6, 200°C, fan 180°C, and boil the kettle. Melt the butter in a large pan over a medium heat. Add the shallots and thyme leaves and cook for 3 minutes until softened. Add the potato slices and stir to coat in the buttery mixture.
Pour in the milk, bring to a simmer, then cover and cook for 7-8 minutes, until the potatoes are just tender.
Meanwhile, wilt the spinach by placing in a colander and pouring over a kettle of hot water. Rinse with cold water. Squeeze out as much liquid as possible. Season then set aside.
When the potatoes are ready, 125ml (4fl oz) crème fraîche. Boil for 2-3 minutes or until the liquid has reduced and thickened. Season well.
Spoon half the potato mixture into a 24 x 21cm (91⁄2in x 81⁄2in) ovenproof dish, scatter over the spinach and haddock and top with the remaining potato mixture. Then spread the remaining crème fraîche over the top layer of potatoes, sprinkle over the Parmesan, and finally the breadcrumbs. Bake for 25-30 minutes, until golden.
See more Main recipes