These lemon meringue squares are a dressier version of a lemon square and are topped with a cooked marshmallow layer.
For a simpler, more traditional lemon square, simply omit the meringue marshmallow layer.
Makes 1 8-inch pan.
Preheat oven to 350ºF and lightly grease an 8-inch square pan and line with parchment paper so that it comes up the sides of the pan. Toss all the crust ingredients until well-combined and press into the prepared pan. Bake for 12 minutes and cool while preparing the lemon filling.
Reduce the oven to 325ºF. Whisk all the filling ingredients together and pour into the cooled crust. Bake for 20 minutes, until set but with a little jiggle in the centre, then cool to room temperature before chilling for at least an hour.
Stir 3 Tbsp of the cold water with the gelatin and the meringue powder in a large bowl or the bowl of a mixer fitted with the whip attachment and set aside.
Bring the remaining 2 Tbsp of water, the sugar and the corn syrup to a boil and boil uncovered and without stirring until it reaches a temperature of 240ºF on a candy thermometer. While whipping, carefully pour the hot sugar into the bowl with the gelatin and whip this on high speed until tripled in volume and cooled, about 5 minutes.
Remove the lemon square from the fridge. Dollop the marshmallow on top of the filling and spread even. Let chill until set.
Use a blowtorch to lightly brown the marshmallow and chill until ready to slice and serve.
The squares will keep for up to 3 days refrigerated.