To make the lemon curd, in a large saucepan whisk together, lemon juice, zest, ½ cup sugar and melted butter. Cook over high heat until the sugar has dissolved.
In a separate bowl whisk together the eggs and the remaining half cup of sugar.
Pour the hot butter, lemon mixture over the eggs and whisk to combine. Pour the mixture, back into the saucepan and using a wooden spoon, stir for 4-5 minutes, over low heat until the mixture is thick and coats the back of the spoon. Transfer the lemon curd to a jar or bowl and place in the fridge to cool.
Preheat the oven to 180°C. Line a muffin tin with papers.
To make the cupcakes, use a food processor to combine all the dry ingredients together. With the motor running pour in the milk, vanilla and eggs. Pour the mixture into cases and fill two thirds full. Bake for 15 minutes until golden and cooked through. Transfer to a cooling rack to cool.
To make the meringue topping, beat the egg whites in a large clean bowl using an electric whisk, until soft peaks form. Add the sugar a tablespoon at a time. Continue to whisk on high speed until the meringue is thick and the sugar is dissolved. Place the meringue in a piping bag, fitted with a 2cm round nozzle.
To assemble, cut a small hole out of the middle of each cupcake. Fill with a teaspoon of lemon curd and pipe over the meringue. Use a kitchen blow torch to gently scorch the meringue.
NOTE: Best eaten on the day they made. Keep leftover lemon curd in an airtight container refrigerated for up to 3 weeks.