Add the cubed butter and rub it into the flour until the mixture resembles breadcrumbs.
Stir in just enough cold water with a knife to bring the mixture together into a dough.
Roll out the dough on a floured surface into a circle about 10 cm larger than the tart tin.
Carefully lift the pastry around a rolling pin and unroll it over the tin.
Press the pastry gently into the corners.
Trim away excess pastry and refrigerate for 30 minutes.
Preheat the oven to 200°C (180°C fan) or Gas Mark 6.
Place a baking tray in the oven to heat.
Heat the oil in a frying pan and gently fry the leeks until soft.
Set aside.
In a mixing bowl, whisk together the eggs, cream, cheese, dill, salt, and pepper.
Spread the cooked leeks evenly over the pastry base.
Scatter the haddock chunks over the leeks.
Pour the cream mixture over the filling, ensuring even coverage.
Place the tart on the preheated baking tray and bake for 25-30 minutes, or until golden brown and set.
Allow to cool slightly before serving.
Notes / Tips / Wine Advice:
Serving Tip:Serve warm with a fresh green salad and a drizzle of lemon juice for extra brightness.Wine Advice:A crisp Chardonnay or a dry Sauvignon Blanc pairs well with the creamy, smoky flavors of this tart.