• 150–200g (5½–7 oz) salt cod, soaked in cold water for about 48 hours – change the water 3 or 4 times during the soaking time (it’s important to try to soak out all the salt)
• about 300ml (10½fl oz) whole milk
• 500g (1lb 2oz) floury potatoes (such as Maris Piper), peeled and cut into large pieces
• 1 garlic bulb, cloves separated, skin on
• 1 rosemary sprig
• 25g (1oz) aged sheep’s or cow’s cheese, finely grated
• 1 egg, plus 1 egg beaten with a little milk for the wash
• 3–4 thyme sprigs
• a knob of butter
• 4–6 tablespoons extra-virgin olive oil
• freshly ground black pepper

For the wholemeal shortcrust pastry

• 300g (10½ oz) plain wholemeal (wholewheat) flour, plus extra for dusting
• 150g (5½ oz) butter, cubed and chilled
• a good pinch of sea salt

First, make the pastry case. Pulse the flour, butter, and salt in a food processor until you have the consistency of breadcrumbs. With the motor running, steadily add 3–4 tablespoons of cold water, stopping as soon as the dough comes together. Remove the dough from the processor, knead it a couple of times, then wrap it and chill it in the fridge for at least 30 minutes.

Rinse the soaked fish, then cut it into cubes, put it in a pan and pour over just enough milk to cover. Bring the liquid up to a gentle simmer and continue to simmer for 5 minutes, or until the fish is cooked through. Drain the fish but reserve the milk. Pick over the fish, discarding the skin and any bones, then whizz the flesh in a food processor. Alternatively, bash the fish in a pestle and mortar until it has a fine texture.

Meanwhile, place the potatoes, garlic and rosemary in a pan, cover with water (no need to salt it), and bring it to a boil. Lower the heat and simmer the potatoes until they’re tender (about 10–15 minutes). Lift the garlic cloves from the water and reserve them, but discard the rosemary. Drain the potatoes and allow them to steam off for a while, then mash them – don’t worry if they’re a bit lumpy, it’s a rustic pie.

Mix the fish and potatoes together with all but a scattering of grated cheese, some freshly ground black pepper and just enough warm, fishy milk to loosen the mixture a little. Crack the egg and fold this in.

Heat the oven to 200°C/180°C fan/400°F/Gas 6.

To make the tart, first remove the pastry from the fridge and leave it at room temperature for 30 minutes. Then, roll out the pastry on a cool, floured surface to a disc 40cm (16in) in diameter and 2–3mm (¹/₁₆–⅛ in) thick. Slide the pastry onto a piece of baking paper, then slide this onto a baking sheet.

Spoon the filling into the middle of the pastry, then fold the pastry edges over to encase it. Carefully peel away the skins from the garlic and arrange the soft cloves over the top. Tear up the thyme sprigs and scatter these over, too. Brush the pastry with a little egg wash, then scatter over the remaining cheese. Give the top a final twist of black pepper and bake the pie for 35 minutes, or until the pastry is golden and crisp. Allow it to cool for 20 minutes before cutting and serving.