Salmon, spinach and dill potato bake

Method

1. Cook the unpeeled potatoes in a pan of boiling water for 15 minutes. Drain and set aside.
2. Meanwhile, put half the spinach in a colander over the sink. Pour over boiling water to wilt the spinach, then refresh in cold water. Repeat with the remaining spinach. Drain and squeeze out as much liquid as possible. Set aside in a large bowl, along with the salmon, onion and lemon zest.
3. Make a white sauce. Melt 50g butter in a pan over a medium heat. Add the flour and cook, stirring, for 1 minute, then gradually whisk in the milk. Cook for 5 minutes, stirring, until thickened. Season, stir in the dill and cool slightly. Pour over the salmon mixture and gently mix. Tip into a deep 2.3-litre baking dish.
4. Remove and discard the potato peel and slice thinly. Overlap in a single layer on top of the salmon.
5. Chill, cover and freeze for up to 2 months. Thaw at room temperature for 8 hours or until fully thawed.
6. Melt the remaining butter and brush over the potatoes. Preheat the oven to 200°C/fan180°C/gas 6. Bake for 50 minutes, or until hot throughout. Serve with peas.