For the Tart Crust:

• Make the Pastry: In a mixing bowl, rub the chilled butter into the flour until the mixture resembles breadcrumbs. Stir in the icing sugar. Add the egg yolk and cold water, mixing until the dough comes together. Alternatively, you can pulse the ingredients in a food processor until combined.
• Chill the Dough: Wrap the dough in cling film and chill in the refrigerator for 30 minutes to firm up.
• Roll Out the Dough: Preheat your oven to 200°C (180°C fan) or 400°F. Roll out the chilled dough on a lightly floured surface to about 3mm thickness. Line a 23cm tart tin with the dough, trimming any excess.
• Blind Bake the Tart Shell: Prick the base of the pastry with a fork, line it with baking parchment, and fill it with baking beans or rice. Bake for 15 minutes, then remove the beans and parchment and bake for another 5-7 minutes until golden. Set aside to cool.

For the Lemon Posset Filling:

• Heat the Cream and Sugar: In a saucepan, combine the double cream and caster sugar. Place over medium heat and stir until the sugar dissolves completely. Bring the mixture to a gentle boil, then reduce the heat and let it simmer for 3 minutes, stirring occasionally.
• Add the Lemon Juice: Remove the saucepan from the heat and allow the cream mixture to cool slightly. Stir in the freshly squeezed lemon juice, mixing well until fully incorporated.
• Strain the Mixture: For a smooth finish, strain the lemon posset mixture through a fine sieve into a pouring jug to remove any zest or undissolved sugar.
• Fill the Tart Shell: Pour the lemon posset mixture into the cooled tart shell, smoothing the top with a spatula. Allow the tart to cool at room temperature for 30 minutes.
• Chill: Once cooled, refrigerate the tart for at least 4 hours, or until fully set.