1. Preheat the oven to 180C (fan-forced). Melt the butter in a large pan over medium heat and add the flour. Using a wooden spoon, beat to a smooth paste (a roux). Take off the heat.

2. Start adding the milk to the roux by beating in about 2 tablespoons at a time, until you have incorporated about a quarter of the milk. Switch to a whisk and gradually incorporate the remaining milk.

3. Return the pan to medium heat, add the bay leaf and simmer for 10 minutes. Whisk frequently to  prevent the sauce from burning on the bottom of the pan. If the sauce becomes too thick (it should have the consistency of custard or a thick tomato sauce), whisk in a little more milk.

4. Remove the bay leaf, season with salt and white pepper (black pepper is fine if you don't mind the speckles), and stir in a heaped tablespoon of grainy mustard and the lemon zest.

5. Stir the smoked fish, boiled eggs and peas through the mixture. Spoon the filling into a medium pie dish (or other ovenproof dish).

6. Slice the zucchini thinly (about 2mm thick) using a mandolin. Arrange the slices over the pie filling in overlapping circles from the centre outwards. 

7. Brush the top with the olive oil and bake for 20 minutes, or until the zucchini slices are golden brown and the mixture is bubbling. Serve with lemon juice.

For something heartier, try Jill Dupleix's fish, prawn and potato pie.