Two-Potato Cheddar & Parmesan Gratin

1. Preheat the oven to 200°C/Gas 6. Grease the PushPan with the butter.
2. Put the potato and sweet potato slices into a large saucepan. Cover with just-boiled water and add a generous pinch of salt. Simmer for 8 minutes, then drain well in a colander. Allow to cool slightly.
3. Arrange a layer of potatoes in the base of the PushPan, season with a little salt and pepper, then arrange a layer of sweet potatoes on top. Sprinkle with a third of the spring onions and herbs, then with a third of each of the two cheeses.
4. Repeat all the layers once more, then finish with a layer of potatoes. Sprinkle the remaining spring onions, herbs and cheeses on top.
5. Transfer to the oven and bake for approximately 30-35 minutes. Cool for 10 minutes in the tin, then remove by positioning the PushPan on a tall jar and pushing down to release. Cut into wedges and serve.

Tip: You can make this recipe without the sweet potatoes if you prefer – just use 1.4kg potatoes instead.