Cooking oil spray, to grease
250ml milk, plus extra 500ml
100g unsalted butter, plus extra 125g softened
1 tsp fine salt
175g gluten-free flour
1½ tsp xanthan gum
5 free-range eggs
8 free-range egg yolks
1½ cups caster sugar, plus extra 1½ cups
½ cup cornflour
1 cup lemon juice
2 tsp finely grated lemon zest
2 Tbsp glucose syrup
½ tsp cream of tartar
Seeds of 1 vanilla bean
Preheat oven to 180 degrees C fan-forced (200 degrees C conventional).
Grease a 20cm round, deep fluted tart tin with oil spray. Combine milk, butter and salt in a medium saucepan, set over medium heat. Simmer for 1 minute. Sift flour and xanthan gum together. Mix into the milk mixture and cook, stirring constantly, for 3 minutes.
Remove from heat and transfer to a stand mixer. Beat with paddle attachment for 3 minutes to cool, then add 2 eggs and 2 yolks and beat until smooth. Transfer dough to a lightly floured bench, then knead for 3 minutes, until smooth. Roll out to 5mm thick, cover with plastic wrap. Chill for 30 minutes.
Roll pastry into a 3mm-thick round, then press into prepared tin. Line with dampened baking paper and baking weights. Bake for 25 minutes, until lightly golden. Remove paper and weights, then bake for 5 minutes more. Set aside to cool.
Put caster sugar and half the extra milk in a medium saucepan. Bring to the boil, then reduce heat to low. Separate 3 eggs. Put remaining milk and cornflour in a bowl and whisk until smooth. Beat into hot milk with extra butter, juice, zest and all the yolks. Simmer, whisking constantly, until thickened. Strain into the pastry case. Chill for 1 hour.
Combine extra caster sugar with glucose syrup and 2 tablespoons water in a small saucepan and set over high heat until a thermometer reads 119 degrees C. Meanwhile, put egg whites and cream of tartar in a large, clean bowl and whisk with an electric hand mixer until soft peaks form. Pour in syrup in a steady stream and whisk on high speed until cooled, then beat in vanilla seeds. Spoon meringue onto lemon curd, then burn lightly with a kitchen blowtorch and serve.