225 g (8 oz/1½ cups) plain (all-purpose) flour
½ teaspoon sea salt
2 tablespoons caster (superfine) sugar
160 g (5½ oz) cold butter, diced
125 ml (4 fl oz/½ cup) chilled water
3 large sweet potatoes, skins on
2 tablespoons ground cinnamon
2 teaspoons ground ginger
1 teaspoon ground mace
1 teaspoon freshly grated nutmeg
½ teaspoon ground allspice
2 teaspoons sea salt
230 g (8 oz/1 cup, firmly packed) light brown sugar
1 vanilla bean, split in half lengthways, seeds scraped
250 g (9 oz) tin sweetened condensed milk
90 g (3¼ oz/¼ cup) golden syrup or treacle, plus extra to serve
1 batch of whipped marshmallow
60 g (2¼ oz/½ cup) pure icing (confectioners’) sugar, sifted
60 g (2¼ oz/½ cup) cornflour (cornstarch)
1 tablespoon liquid glucose
450 g (1 lb/2 cups) caster (superfine) sugar
3 egg whites
7 g (¹⁄6 oz) sachet powdered gelatine
To make the dough, process the flour, salt and sugar in a food processor until pea-sized crumbs form. Add the butter in batches, pulsing to a granular consistency. Turn out into a bowl. Add the chilled water in batches, mixing by hand until the dough is just combined. Wrap in plastic wrap and refrigerate for 1 hour. Roll out the dough on a floured surface to about 3 mm (¹⁄8 inch) thick. Press into a 24 cm (9½ inch) floured pie dish, or into six 10 cm (4 inch) floured dishes. Trim off the excess, then crimp the edge and prick the base with a fork. Freeze for 15–20 minutes, to solidify the butter in the pastry.
Meanwhile, start preparing the filling. Preheat the oven to 180°C (350°F). Put the sweet potatoes on a baking tray and bake for 45 minutes to 1 hour, or until tender. Remove from the oven and leave to cool.
Turn the oven down to 160°C (315°F). Cover the dough with a sheet of baking paper, then weigh the paper down with baking beads, dried beans or uncooked rice. Blind bake a large pie for 25–30 minutes, and the smaller ones for about 15 minutes, or until the pastry is golden.
Meanwhile, finish off the filling. Cut the sweet potatoes in half and scoop the flesh into a food processor. Add the spices, salt, sugar and vanilla seeds and purée until smooth. Add the eggs one at a time, then the condensed milk — the batter should be thick, not runny.
Turn the oven down to 150°C (300°F). Pour the filling into the pre-baked pie crust and bake for 45 minutes, or until set into a custard. Drizzle with the golden syrup and bake for a final 15 minutes. Remove from the oven and leave to cool for 30 minutes.
To prepare the whipped marshmallow, spray a baking dish with cooking oil, then dust with 1 tablespoon of the icing sugar. Put the remaining icing sugar in a large bowl, mix the cornflour through and set aside for dusting the marshmallow. Combine the liquid glucose, caster sugar and 200 ml (7 fl oz) water in a saucepan and heat until the sugar has dissolved. Continue cooking until the mixture reaches 120°C (250°F) on a sugar thermometer. Meanwhile, using an electric mixer fitted with a whisk attachment, beat the egg whites until stiff peaks form. Now gradually add the hot glucose syrup; when all the sugar is incorporated, the egg whites will be shiny, tacky and fluffy. Continue whipping for 10 minutes on high speed until the mixture is cool.
Top the pie with the whipped marshmallow, using a spatula to create meringue-like peaks. Now refrigerate the pie for at least 4 hours, to set the marshmallow and filling. Torch the marshmallow topping with a kitchen blowtorch until golden brown, as you would a meringue. Enjoy the same day, drizzled with extra golden syrup.