Ingredients

Topping
700g (about 4 medium) floury potatoes, peeled and sliced very thin (2–3mm, ideally on a mandolin)
40g melted butter (or olive oil for brushing)
Salt & pepper
A handful of Gruyère to top (optional)

Filling
40g butter
1 medium onion, finely chopped
2 leeks, thinly sliced
40g plain flour
500ml Freja fish bone broth
125ml whole milk
200ml cream
1 tsp wholegrain mustard
120g Gruyère, grated
3 boiled eggs, halved
250g white fish (cod or haddock), cut into chunks
150g smoked fish (e.g. smoked haddock), cut into chunks
150g salmon, cut into chunks
150g raw peeled prawns
Handful of parsley, chopped
Zest of ½ lemon
Salt & pepper

Method
1. Melt the butter in a large ovenproof skillet or pan over medium heat. Add the onion and leek, cooking until softened, about 5–6 minutes.
2. Stir in the flour and cook for 2–3 minutes to form a roux.
3. Gradually whisk in the fish bone broth, a little at a time, ensuring it stays smooth. Once incorporated, add the milk and cream. Bring to a gentle simmer and cook for 8–10 minutes, stirring often, until thickened and glossy.
4. Stir in the mustard, three-quarters of the cheese, the parsley, and lemon zest. Season generously with salt and pepper.
5. Remove from the heat and gently fold in the white fish, smoked fish, salmon, and prawns. Spread the filling evenly in the pan.
6. Place the boiled eggs on top, gently pressing into the sauce
7. Arrange the potato slices neatly over the filling in overlapping layers, like fish scales. Brush each layer lightly with melted butter and season with salt and pepper as you go.
8. Finish with a final brush of butter and scatter the remaining cheese over the top.
9. Bake in a preheated oven at 180°C fan for 40–50 minutes, until the potatoes are golden and crisp and the filling is bubbling at the edges.
10. If the potatoes need extra browning, finish under the grill for 2–3 minutes.
11. Rest for 5 minutes before serving straight from the skillet with crunchy green vegetables on the side.