1 small leek, outer leaves removed, the white thinly sliced on an angle
150ml whole milk
140g piece haddock fillet, skinless and boneless
1 tsp black peppercorns
2 bay leaves
250g puff pastry
Flour, for dusting
1 egg
120ml double cream
1 tsp mustard powder
Finely grated zest of ½ lemon
10g tarragon leaves, chopped
85g tin smoked oysters, drained and each oyster cut in half
Heat the oven to 200C/390F/gas mark 6. In a bowl, mix the sweet potato with a tablespoon of oil, a quarter-teaspoon of salt and a little black pepper. Tip on to a small baking tray and roast for 20-25 minutes, until cooked and starting to brown. Tip back into the bowl, add the maple syrup, mash roughly and set aside.
Heat the remaining oil in a medium sauté pan on a medium flame. Add the leek, an eighth of a teaspoon of salt and a little black pepper, fry for four minutes, stirring, until cooked, then tip into a bowl.
Give the sauté pan a wipe, then add the milk, haddock, peppercorns and bay leaves. Bring to a simmer, cover and cook for four minutes, until the fish flakes when touched. Remove from the heat, set aside to cool, then lift out the fish with a slotted spoon and break into a bowl, in roughly 2cm pieces. Cover and refrigerate; discard the milk and aromatics.
Turn down the oven to 180C/350F/gas mark 4. On a lightly floured surface, roll out the pasty to 2mm thick, then cut into circles to fit six 8cm-diameter, crinkle-edged tart cases with removable bases. Press the pastry into the moulds, trim the edges and prick all over with a fork. Place baking paper discs in each and fill with baking beans. Transfer to a baking tray, rest in the fridge for 10 minutes, then bake for half an hour. Remove the paper and beans, bake for 10 minutes more, until turning golden brown, then set aside to cool.
While the tart shells are cooking, put the egg, cream, mustard, lemon zest and chopped tarragon in a bowl with an eighth of a teaspoon of salt and a grind of black pepper. Whisk to combine, then pour into a small jug.
Spoon a 3mm-thick layer of sweet potato mash into each tart base. Dot the oyster halves on top, followed by the haddock and leek: you want to be able to see everything. Divide the cream between the tarts, then bake on the top shelf of the oven for 20 minutes, until set. Leave to rest for five minutes, then serve.
