In a large bowl, whisk together the gluten free flour blend, sugar, xanthan gum and salt.

Add the cubed cold butter and toss it in the dry ingredients. Using your fingertips or a pastry cutter, work the butter into the dry ingredients until it's about the size of walnut halves.

Start adding the cold water, about 1 tablespoon at a time. After each addition, use your fingertips or a fork to toss the mixture around so that the flour gets evenly hydrated. Continue adding the water and tossing the mixture until all the flour has been hydrated and the mixture starts clumping together in places. It might still look crumbly at this point. Tip: Depending on your gluten free flour blend, you might need slightly more or less water than is listed in the recipe. If there are any patches of dry flour, sprinkle them with some extra cold water.

Bring the pie dough together into a ball by giving it a gentle knead and pressing it against the sides of the bowl. Your dough won’t look perfectly smooth at this stage – it will look slightly “shaggy” and uneven, with a few cracks here or there. Be careful not to overwork it, as that can cause the butter to start melting due to the heat from your hands, which can reduce the flakiness of the final pastry.

Wrap the pie dough in plastic wrap/cling film, and chill it in the fridge for at least 30-45 minutes.

On a lightly floured work surface, roll out the chilled pie dough into a long rectangle about ¼ inch (about 5-6mm) thin. The exact dimensions of the rectangle aren’t important, aim for a length that’s about three times the width.

First letter fold: Fold one third of the rectangle towards the centre and then fold the other third over it (as you would a letter).

Rotate the folded pastry by 90 degrees, so that the open ends point towards and away from you, and roll it out again into a long rectangle.

Second letter fold: Fold one third of the rectangle towards the centre and then fold the other third over it (as you would a letter).

Wrap the finished pie dough tightly in plastic wrap/cling film and chill it in the fridge for at least 30 minutes.

Get a 9-inch (23cm) pie dish ready to have on hand, it should be about 1½ inches (4cm) deep.

Roll out the chilled pie dough into a rough circle about 12 inches (30cm) in diameter and about ⅛ inch (3mm) thin. Transfer it to the pie dish, making sure that it’s snug against the bottom and sides. Trim the excess dough, leaving about a 1 inch (2.5cm) overhang.

Fold the overhanging dough under itself and crimp the edges.Tip: To crimp the edge, form a V-shape with the thumb and index finger of your non-dominant hand on the outside edge of the pie crust. Then, use the index finger of your dominant hand to push the pastry into that V-shape. Move around the edge of the pie crust to create a fluted rim.

Chill the assembled pie crust in the fridge for at least 30 minutes.

While the pie crust is chilling, pre-heat the oven to 400ºF (200ºC) with a large baking sheet on the lower middle oven rack.

Dock the bottom of the chilled pie crust with a fork, line it with a sheet of parchment/baking paper paper and fill it to the brim with pie weights (rice or dried beans work too).

Place the pie dish directly on the hot baking sheet and blind bake for 18-20 minutes or until the edges are light golden.

Remove the pie weights and parchment/baking paper, and bake for a further 10-15 minutes or until the pastry is crisp and evenly golden brown with slightly darker edges.

Allow the pie crust to cool completely in the pie dish.

It's best to minimise contact with metal when preparing the lemon filling to prevent it from developing a metallic aftertaste. Therefore, I don't recommend using a metal bowl, metal utensils (such as a metal whisk) or a metal/metal-coated saucepan.Instead, use a glass or ceramic bowl, a rubber spatula or a wooden spoon, and a non-metal saucepan such as one with a ceramic coating.

Add the sugar and lemon zest to a large bowl, and use your fingertips to rub the zest into the sugar.Tip: This helps to release more essential oils from the zest and it will make your lemon filling extra fragrant.

Add the egg yolks and egg to the lemon-sugar, and mix or whip them until slightly fluffy and paler in colour (no need to use a stand or a hand mixer for this, just whisk them briefly together by hand with a silicone whisk, a rubber spatula or a wooden spoon).

Add the cornstarch (US)/cornflour (UK) and mix well to combine.

In a saucepan over medium-high heat, cook the water and lemon juice until they only just come to a boil.

Add the hot lemon juice-water mixture to the egg-sugar mixture in a slow stream, mixing constantly until you've added all the liquid.Tip: This tempers the eggs and reduces the chances of your lemon filling splitting or curdling when you cook it.

Return the mixture to the saucepan and cook it over medium heat with constant stirring until thickened and it comes to a boil (you should see large bubbles popping up, this should take about 4-5 minutes) and then cook for 1-2 minutes longer.Tip: For cornstarch (US)/cornflour (UK) to achieve its maximum thickening power, the mixture has to come to a boil and stay there for some time – one or two minutes in this case. This results in a very stable lemon filling that holds its shape beautifully so you can cut neat, clean slices.

Remove from the heat and stir in the butter until it's fully melted.

Pass the lemon filling though a fine mesh sieve to remove the lemon zest – this will make it perfectly smooth and creamy (but you can skip this step if you don't mind the texture of the lemon zest).Tip: I don't recommend using a metal sieve, as contact with metal can give your lemon filling a slight metallic aftertaste. If possible, use a sieve with a plastic or silicone mesh.

Pour the finished lemon filling into the cooled blind-baked pie crust and smooth it out into an even layer. Place a sheet of plastic wrap/cling film on top, so that it's in direct contact with the surface of the lemon filling – this will prevent skin formation.

Allow to cool completely to room temperature, then chill in the fridge for at least 4 hours or overnight.

It's best to prepare the Swiss meringue topping as close to serving as possible.

Combine the egg whites, sugar and cream of tartar in a heat-proof bowl above a pot of simmering water. Heat the meringue mixture with constant whisking until it reaches 160ºF (70ºC) and the sugar has fully dissolved.

Remove from the heat, transfer to a stand mixer fitted with the whisk attachment (or use a hand mixer fitted with the double beaters) and whisk for 5-7 minutes on a high speed setting, until greatly increased in volume and stiff peaks form.

Add the vanilla and whisk until well combined.

Spoon the Swiss meringue on top of the chilled lemon filling and use a small offset spatula or the back of a spoon to shape it into a mound, creating a few decorative swirls and swoops.

Use a kitchen blow torch to toast the Swiss meringue, then slice and serve.

The gluten free lemon meringue pie is at its best on the first day, but it keeps well in a closed container in the fridge for 2-3 days.