By hand

Stir the flours and salt together in a bowl. Using your fingertips, rub in the butter until the mixture looks like fine breadcrumbs.

Use a round bladed knife to stir in the grated Parmesan.

Gradually add enough cold water, 1 tbsp at a time and stirring in with the knife, until the pastry starts coming together.

Using a food processor

Put the flour, salt and butter into the food processor and whizz until the mixture looks like fine breadcrumbs.

Add the grated Parmesan then briefly whizz to incorporate it into the mixture.

With the motor still running add cold water, 1 tbsp at a time, until the pastry starts coming together.

Turn out onto a lightly floured surface and gently knead into a smooth ball.

Flatten into a disc then wrap in foil or cling film and chill in the fridge for at least 30 minutes.

Peel or scrub the potatoes and cut into chunky dice.

Put in a saucepan, cover with cold water and add salt to taste. Bring to the boil then turn down to a simmer and cook until just tender.

Drain and leave to dry and cool in the colander/sieve.

Put the olive oil in a medium frying pan over medium heat.

Top and tail the leeks then cut into thinnish slices. Rinse well under running water to remove any mud, drain, then add to the frying pan.

Season with a little salt and pepper then sauté until soft, adding the chopped garlic for the final few minutes.

Add the spinach to the pan, stirring around until it's wilted and any water is evaporated.

Take the pan off the heat and stir in the butter and cream cheese so they melt and mix with the rest of the ingredients.

Stir in 50 g of the grated Cheddar.

Gently stir in the cooked potatoes, trying not to break them up.

Taste the filling and add more salt and/or pepper if necessary.

Set aside to cool.

Divide the chilled pastry into 4 equal pieces, using scales for accuracy.

Work with one piece at a time, keeping the rest covered so they don't dry out.

On a lightly floured surface, roll into a circle big enough to come all the way up the sides of a pie tin, but not so big that you need to cut any off. Neaten the top edge by pressing down and smoothing with your fingers, then put in the fridge to chill for 30 minutes: this is important so the pastry doesn't shrink as it cooks.

Repeat with the remaining pastry.

Preheat your oven to 220°C /200°Fan /Gas 7 /425°F.

Divide the filling between the chilled pastry cases. Try to fill any gaps, but don't press the filling down or compact it. To fit all the filling in you'll need to pile it up, but that's how it should be.

Sprinkle the tops with the remaining 50 grams of grated Cheddar.

Place the pies on a baking tray and transfer to a middle shelf of the oven.

Cook for 20 minutes or until the pastry is browned and crisp and the filling hot and deep golden.

Rest for a few minutes before carefully taking out of the pie tins.

Can be eaten hot or cold.

Store in the fridge for 3 days or can be frozen.

Reheat in a microwave, medium oven, or air fryer.

Recommended: briefly heat in a microwave to start heating the filling, then air fry on 'bake' to re-crisp the pastry.