In a large bowl, rub the butter and flour together using your hands until it resembles coarse breadcrumbs. Stir in the xanthan gum and a large pinch of salt. In a small bowl, combine the egg yolk and 1 tbsp of cold water. Add the egg mixture to the flour and, using a knife, stir to combine until it starts to come together. If still a bit crumbly, add a drop more cold water a tsp at a time. Bring together into a disc, using your hands and wrap in cling film. Place into the fridge to chill for at least 30 mins.

When ready to use, roll out between two sheets of greaseproof paper to the thickness of a pound coin. Remove the top sheet of paper and carefully flip into the tin, with the remaining greaseproof paper facing up. Remove the remaining paper and reserve. Press the pastry into the base and sides of the tin. It may crumble, but you can patch up any holes with the remaining pastry. Trim the sides and place to rest in the fridge for 30 mins to firm up.

Heat the oven to 180°C/160°C fan/gas 4. Scrunch up one of the reserved sheets of greaseproof and carefully press into the pastry. Fill with baking beans, making sure they go up the sides as well. Place onto a baking tray and blind bake for 15-20 mins until the edges are starting to turn golden and the base is set. Remove the baking beans and greaseproof paper and bake for a further 5-10 mins until the base feels dry. Remove to a wire rack to cool, then fill as you like.