Prepare the Crust:

• Preheat oven to 350°F (175°C). Line a 9-inch square baking pan with aluminum foil, leaving an overhang for easy removal. Lightly coat with cooking spray.

• In a bowl, mix shortbread crumbs and melted butter until evenly moistened. Press firmly into the prepared pan.

• Bake for 14 minutes, until edges start to turn golden.

Make the Lemon Filling:

• While the crust bakes, whisk together sugar, salt, and lemon zest in a medium bowl.

• Add lemon juice and whisk until combined.

• Add eggs and whisk until smooth.

• Once the crust is done, pour the lemon mixture over the hot crust.

• Bake for 18-22 minutes, until the edges are set but the center is slightly jiggly.

• Let cool at room temperature, then cover and refrigerate for at least 3 hours or overnight.

Prepare the Marshmallow Meringue:

• When ready to serve, bring 2 inches of water to a simmer in a saucepan.

• In a heatproof bowl, combine egg whites and sugar, then place over simmering water. Whisk constantly for 5-7 minutes, until it reaches 140°F (60°C) and the sugar is dissolved.

• Transfer to a stand mixer with a whisk attachment and beat on medium-high speed for 5-7 minutes, until stiff peaks form.

Assemble & Toast the Meringue:

• Lift chilled bars from the pan using the foil overhang.

• Spread the meringue over the top, making decorative swirls.

• Torch Method: Lightly toast the meringue with a kitchen torch until golden.

• Broiler Method: Place under a broiler for 1-2 minutes, watching closely to prevent burning.

• Use a sharp knife to cut into squares. For the cleanest cuts, dip the knife in hot water and wipe it dry between slices.

• Serve immediately or within a few hours for the best texture.